The verses you quote do not address the OP.
The OP makes it clear that both Paul and Peter wrote epistles to the Galatians.
Paul told the Galatians that if anyone preaches a different gospel, they are to be accursed.
Peter tells the Galatians that Paul had previously wrote letters to them.
Yet, you want us to believe that after Paul wrote letters to the Galatians, Peter came and preached a different gospel to them.
If what you claim is true (it's not), then the Galatians would have had to accurst Peter based on what Paul told them.
Actually, all the passages we quote address these issues - because the passages are all interrelated.
The problem is that you have been so conditioned by the reasoning your books supposedly about the Bible have turned into a truth, add to this, that you have no actual Bible in you as a result, that yours is reading into the passages, such notions as "Christ returned in 70 AD via the Romans Army," that you are simply unable to see the answers you supposedly want, in the passages we post.
To this you then add the projection that we get this from books.
Yours is the autobiography of your failure projected onto others.
You well know you get your reasoning from books. You and yours all do this.
Your books based reasoning has left you that blind - you cannot see that you are projecting your notion of "learn about the Word from books" as the practice of all who do not agree with you.
Bad enough your notion of "Christ returned in 70AD via the Roman Army" is heresy.
Fact of the matter is that Galatians 1's "another gospel, which is not another" of the same kind, is the issue of a gospel that was neither Peter's nor Paul's.
Rather, it was a fusion of Law with Grace into another gospel, which was not another at all, and this was only part of the issue.
Not sure what your problem is, but it sure does not come across as any kind of an appeal fro the truth of these issues.
It comes across as more just one more example of someone else out there as bad off in his approach towards others where they differ with one's own, no matter what it is they are asserting is the truth.
You and yours in this biting and devouring spirit - regardless of what field and or truth you each assert is the truth of a matter - are all over the net.
Darby is not your issue. We are not your issue. Truth is not your issue.
Issue is your issue, you fool.