What is very clear indeed is Paul and Barnabas were separated to bring the Gospel to the Gentiles (and still offer it to the Jews). What has not been established is that it was a different gospel.
In Acts 15, as I pointed out there was not a debate on the nature of the Gospel but a Judaizer influence which contrasted the Gospel. That was the dispute. Given the text of Acts 15 it is clear their is agreement that Peter and others were preaching the same Gospel as Paul. Peter as I point out earlier makes this statement based on his experience with Cornelius and tells us they were saved by Grace. So if we conclude a dispensation change comes out of the council then we would conclude Peter ushered it in with his presentation to Cornelius and household. The context of Peters testimony tells us this.
So if the Gospel preached to Cornelius by Peter as stated:
Acts 15:8-9 NASB
And God, who knows the heart, testified to them giving them the Holy Spirit, just as He also did to us; and He made no distinction between us and them, cleansing their hearts by faith.
Since Peter states there is no distinction between Cornelius and them, meaning Peter and Jews assembled, then those saved prior to that time received the same Gospel.
As stated before, no where earlier in Acts do we see Peter or any other apostles teach or command circumcision or any other ceremonial laws as a call to salvation or required observances. No such gospel, dispensation or program is mentioned at all. By the Acts account and Galatians account the conclusion that is best arrived at is there was a false or evil influence that was perverting the true gospel.
We can assume that the Jerusalem church Jews were still observing elements of the law, but not replacing Christ as Messiah. They most likely still circumcised their sons as sons of Abraham; still observed the Sabbath, feasts etc.but doing so because they saw it as acts of obedience and not works of man-made righteousness unto works of salvation. That is the conflict of the council. There were Judaizers who wanted to impose this on everyone as a requirement for salvation not just the Gentiles. Peter makes it clear they were all saved by Grace Jew and Gentile no distinction.
The dispute during the council at Jerusalem was among the apostles and Peter as well. If all the apostles had been teaching the same thing as Paul there would have been no dispute or the apostles and Paul would simply have said something like “that’s not what we have been teaching you guys” and the issue would have been over. James had to stand and make a declaration which finally put them all on the same page.