The idea that it is Acts that is the least accurate is based mainly on Paul's account being first person and Acts not. Historians apparently prefer accounts from people who were there to those of anonymous people who were not.
And do we have any evidence that, though written in the first person, he didn't dictate the letter of Galatians to an associate? If we look at Galations 6, we see verse 11 says "See with what large letters I am writing to you with my own hand." There are similar passages at the end of several of his letters (and not only the ones that are regarded as legit.), and sometimes it seems to indicate that he has written the last section himself as opposed to having dictated the rest.
Regarding his not having been to Jerusalem before his conversion, from where would he have obtained his credentials to persecute the early Christians if not from the higher Jewish authorities
Why would he need credentials?
In order to arrest Jews who had converted to the new faith, Paul would have reported to the Jewish leaders of each town/city on his arrival - and would have had to have credentials or some other form of identification given him by the Jerusalem authorities.
According to Paul's account in Galatians, he didn't go there before his conversion.
What it says in Galatians is that, having had his conversion experience, he didn't go to Jerusalem for some 3 years. Instead, he
... went into Arabia. Later I returned to Damascus.
Then after three years, I went up to Jerusalem to get acquainted with Cephas (ie Peter) and stayed with him fifteen days. I saw none of the other apostles – only James, the Lord’s brother.
He makes no reference as to whether or not he had been to Jerusalem and the Jewish authorities before his conversion.
Just because Paul doesn't mention such a visit doesn't mean that he didn't make one. In fact, in view of the centrality of visits to Jerusalem to Jewish religious thinking, we can logically assume that he made at least one such visit - perhaps several - before his conversion.
So it is your claim that Paul's account is unreliable. Fair enough, that is a legitimate view.
No, I am not suggesting that Paul's account is unreliable; rather, having read your latest post, I think we are speaking at cross-purposes. You take his statement in Galatioas to mean that he hadn't been to Jerusalem at all before his conversion: I take it to mean that he didn't go to Jerusalem to talk to the apostles until 3 years after his conversion. There is a massive difference between these interpretations, and I'd suggest that yours doesn't actually match with what is written in Galatians.