HJ-3b extension:
Later interpolations in '1Thessalonians' and 'Hebrews', plus dating of 'Galatians'

A) 1Th2:14-16 is an obvious post-70C.E., post-gospel and anti-Jewish addition, which Paul could not have written:
"... the Jews [of Jerusalem], who killed the Lord Jesus and the prophets
[as in Mt23:34,37; Lk11:49-50,13:34 "Jerusalem, Jerusalem, that is killing the prophets ..." (YLT)]
' and also drove us out ... They ... are hostile to all men. ... In this way they always heap up their sins to the limit. The wrath of God has come upon them to the uttermost.
[reference to the events of 70C.E. (as in Mt21:40-41a) which occurred twenty years after the letter was written!]"
Remarks:
a) Nowhere else did Paul write Jesus was "killed", but in the gospels, the word 'kill(ed)' (Greek root 'apokteino'), concerning Jesus, is used many times, as in GMark 8:31, 9:31, 10:34, 12:7,8 & 14:1.
b) The words 'countrymen' (Greek root 'sumphuletes'), 'drove out' (Greek root 'ekdioko') and 'hostile' (Greek root 'enantios') are never in evidence elsewhere in Paul's (authentic) letters.

Note: both 'apokteino' and 'ekdioko' show in Lk11:49, relative to prophets and apostles: "... I will send to them prophets and apostles, and of these shall they [teachers of the Law] kill and drive out by persecution" (Darby)

B) 1Th1:10 is another addition:
"and to wait for his Son from heaven, whom he raised from the dead -- Jesus, who rescues us from the coming wrath."
Why?
a) 1Th1:10 considerably extends a sentence, when Paul used generally short ones in this letter.
b) 1Th1:10 affirms "he raised [Jesus] from the dead" when later, it is a matter of faith "we believe that Jesus died and rose again" (4:14a)
c) 1Th1:10 is packed with theological tenets, some of them having no counterpart in the letter:
Jesus is Christ (1:1,3,2:6,3:2,4:16,5:9,18,23,28) or/and Lord (1:1,3,2:19,3:11,13,4:1,2,15,16,17,5:2,9,23,28), but never "Son". The expressions:
"God the Father and the Lord Jesus Christ" (1:1)
"our God and Father" (1:3,3:13)
"our God and Father himself and our Lord Jesus" (3:11)
And NOT "... the God and Father of our Lord Jesus Christ ..." (2Co1:3a & Ro15:6),
tend to preclude Paul had then Jesus as the "Son".
Then in this letter, dead are risen (4:14,16) (Greek root 'anistemi'), but never "raised" (root 'egeiro').
d) Paul would not have acknowledged "to wait" as a good thing when he wrote in the same letter:
"And we urge you, brothers, warn those who are idle" (5:14)
Apparently, these "idlers" were a problem in the community:
1Th4:11-12 "Make it your ambition to lead a quiet life, to mind your own business and to work with your hands, just as we told you, so that your daily life may win the respect of outsiders and so that you will not be dependent on anybody."

2) Latter interpolations in 'Hebrews'

A) The last Chapter (13) appears to be an addendum, but may contain a later but authentic (very short) letter (or rather note) by Apollos:
Heb13:1-6,
Heb13:9-16 "... Let us, then, go to him outside the camp, bearing the disgrace he bore [Jesus' crucifixion]. For here we do not have an enduring city [Jerusalem, still existing!], but we are looking for the city that is to come ..."
Heb13:18-20a,
Heb13:21-22 "... Brothers, I urge you to bear with my word of exhortation, for I have written you only a short letter ..."
Heb13:25.
However, additions were inserted in it later on (around 100C.E.):
Heb13:7-8 "Remember your [now deceased!] leaders, who spoke the word of God to you ..."
Heb13:17 "Obey your [new!] leaders and submit to their authority..."
Heb13:20b,24a "... your leaders ..."
No community "leaders" are mentioned in the rest of 'Hebrews'.

B) On the subject of addition, it is rather obvious that the following verses is also one of those:
Heb9:27-28 "Just as man is destined to die once, and after that to face judgment, so Christ was sacrificed once to take away the sins of many people; and he will appear a second time, not to bear sin, but to bring salvation to those who are waiting for him."
a) "Just as a man is destined to die once, and after to face judgment":
Judgment to follow death is never a concept exposed in this letter. Rather, the author emphasized his contemporary faithfuls were living in the "last days" (1:2) and destined to enter "Today" (4:7) God's rest (4:6,11) very soon "in just a very little while" (10:35-39) as "you see the Day approaching" (10:25). Then the Judgment would be applied to only the (alive) sinners and/or defectors (10:26-27,30-31,39).
b) Here Christ is offered for sacrifice but in the rest of the letter, it is Christ who is offering himself for sacrifice, such as in:
Heb7:27b "for this He [Jesus] did once for all when He offered up Himself."
Heb10:5-10 and
Heb10:12 "But this Man [Jesus], after He had offered one sacrifice for sins forever, sat down at the right hand of God"
c) "he [Christ] will appear a second time" seems to have been written to "correct" "he [Christ] has appeared once for all at the end of the ages" (10:26), only two verses earlier.
In 'Hebrews' Christ has no role to play during the "Day of the Lord":
God administers the final Judgment (10:30-31,12:23), delivers the rewards (11:40) and disposes of Christ's enemies (1:13). Meanwhile, "Since that time [the sacrifice on the cross] he [Christ] waits for his enemies to be made his footstool" (10:13).
Then, the Christians, through raptures, are to join Christ, God and angels in the heavenly Jerusalem (12:22-24). No second coming here!
However the "second coming" (on earth) will be prominently featured later on (Mt25:31-32, Ac1:11, Rev19:11-16).

Note: the notion of "second coming" did not start immediately among Gentile Christians. Paul had only a half way second coming of Jesus, down to the clouds below heaven (1Th4:16-17). This is echoed in GMark (13:26-27).

3) Dating of 'Galatians'

The dating of 'Galatians' has been proposed anywhere from 48 to 58C.E. My late dating is based on:

A) Gal2:10 "All they [the "Nazarene" leadership] asked was that we should continue to remember the poor,
[collect "survival" money for the church of Jerusalem: 1Co16:1-4, 2Co8-9, Ro15:25-27]
` the very thing I was eager to do.
[and not "am eager to do" or "will be doing"]"
That would suggest all the money collections have been done already when the epistle was written (consequently after '2Corinthians', when they were still in progress). These collections were completed in late 57 or early 58C.E. in Asia minor, Macedonia and Greece. For the Galatians, it was done in early 55 (1Co16:1).

Note: details on the dating are according to my study, as explained in Appendix B (28) and Paul and the Corinthians

B) Eligibility of Gentiles (and Jews) in the Christian church & for salvation, with calls for dumping the law of Moses, is the major theme that 'Galatians' & 'Romans' (written early 58C.E.) have in common and was probably the major issue that Paul had to face then, as corroborated in 'Acts':
Ac21:21 "... you [Paul, months after he wrote 'Romans'] teach all the Jews who are among the Gentiles to forsake Moses. ..."
That would indicate 'Galatians' and 'Romans' were written at about the same time.

C) Other similarities with 'Romans' (they are many!):
a) Mentions of 'Abraham':
Gal3:6 "just as Abraham "believed God, and it was accounted to him for righteousness.""
Gal3:8 "preached the gospel to Abraham beforehand, saying, "In you all the nations shall be blessed."" also 3:7,9,14,16,18, 4:27 (8)
Ro4:1,2,3 "For what does the Scripture say? "Abraham believed God, and it was accounted to him for righteousness.""
Ro4:16 "Abraham, who is the father of us [Christians] all (as it is written, "I have made you a father of many nations")"
also 4:9,12,13, 9:7, 11:1 (9)
The only other occurrence of 'Abraham' in all the Pauline letters is in 2Co11:22.
b) Christians or Christ as seed of Abraham:
Gal3:16,19,29 (3)
Ro4:13,16,18 (3)
This does not show in the other Pauline letters.
c) Mentions of 'Isaac':
Gal4:28 "Now we, brethren, as Isaac was, are children of promise."
Ro9:7-8 ""In Isaac your seed shall be called." ... but the children of the promise are counted as the seed."
'Isaac' does not appear in the other Paul's letters.
d) Mentions of 'sons of God':
Gal3:26 "For you are all sons of God through faith in Christ Jesus."
also 4:5,6,7 (4)
Ro8:14 "For as many as are led by the Spirit of God, these are sons of God."
also 8:19, 9:26 "... sons of the living God." (3)
In Paul's other letters, there is only one mention of "sons of God" (2Co6:18, as a quote).
e) Mentions of '(un)circumcised' and '(un)circumcision' (multiple occurrences in one verse not indicated):
Gal5:2,3 "And I testify again to every man who becomes circumcised that he is a debtor to keep the whole law"
Gal5:6 "For in Christ Jesus neither circumcision nor uncircumcision avails anything"
also 2:3,7,8,9,12, 5:11, 6:12,13,15 (12)
Ro2:25 "but if you are a breaker of the law, your circumcision has become uncircumcision."
Ro3:30 "there is one God who will justify the circumcised by faith and the uncircumcised through faith."
also 2:26,27,28,29, 3:1, 4:9,10,11,12, 15:8 (12)
In the two Corinthians letters, these words occur in only two verses:
1Co7:18-19 "Was anyone called while circumcised? Let him not become uncircumcised [let him stay Jew]. Was anyone called while uncircumcised? Let him not be circumcised. Circumcision is nothing and uncircumcision is nothing, but keeping the commandments of God [part of the law of Moses] is what matters."
Let's notice the progression from '1Corinthians' to 'Galatians' & 'Romans'!
f) Mentions of 'law':
Gal2:16,19,21, 3:2,5,10,11,12,13,17,18,19,21,23,24, 4:4,5,21, 5:3,4,14,18,23, 6:2,13 (25)
Ro2:12,13,14,15,17,18,20,23,25,26,27, 3:19,20,21,27,28,31, 4:13,14,15,16, 5:13,20, 6:14,15, 7:1,2,3,4,5,6,7,8,9,12,14,16,21,22,23,25, 8:2,3,4,7, 9:4,31,32, 10:4,5, 13:8,10 (53)
In 'Galatians' & 'Romans', the law of Moses is most often described as a curse or bringing death & sin, all of which rid by Christ.
Gal2:16b "... for by the works of the law no flesh shall be justified."
Gal2:21 "... for if righteousness comes through the law, then Christ died in vain."
Gal3:10a "For as many as are of the works of the law are under the curse ..."
Gal3:13a "Christ has redeemed us from the curse of the law ..."
Ro3:20 Darby "Wherefore by works of law no flesh shall be justified before him; for by law [is] knowledge of sin."
Ro7:8b-9a "For apart from the law sin was dead. I was alive once without the law, but when the commandment came, sin revived and I died."
Ro8:2 "For the law of the Spirit of life in Christ Jesus has made me free from the law of sin and death."
Ro10:4 "For Christ is the end of the law for righteousness to everyone who believes."
But in the two Corinthians letters, where 'law' occurs in seven verses only, the law of Moses is not described in unfavorable terms (except in 1Co15:56, most likely a later interpolation. See here for explanations). More, it is even quoted by Paul in order to serve his purpose, twice (1Co9:8-9 & 1Co14:21)!
1Co9:8-9 "Do I say these things as a mere man? Or does not the law say the same also? For it is written in the law of Moses, ..."
g) God sending his (pre-existent) Son as a human:
Gal4:4 YLT "... God sent forth His Son, come of a woman ..."
Ro8:3 YLT "... God, His own Son having sent in the likeness of sinful flesh ..."
Only in these two epistles God is said to have sent his Son.
h) The word 'Scripture(s)' appears only in Galatians' (3:8,22;4:30) and 'Romans' (1:2;4:3;9:17;10:11;11:2;15:4;16:26), and not in any other authentic epistles (the two occurrences in '1Corinthians' are the result of interpolation: see my page on '1cCorinthians' for explanation).