What would have happened if Paul's gospel had not been received by the Jerusalem apostles? Would it be possible, since they are all recognised as prophets? Paul thought is was possible, since he deliberately met with the apostles in private in case it went badly.
What happens if apostles disagree? If prophets disagree? Is it possible?
We have a few examples in the Bible of sinful prophets: Balaam, Jonah, the man of God in kings who eats when he shouldn't, Caiphas, Judas. So it is possible to have a true message from God and then fall away.
Moreover, 1Corinthians 14 tells us that the 'spirit of prophets is under the control of prophets'. So they are able to abandon or deny their true message.
Perhaps then, there would have been some pretty hardcore apostolic discipline taking place in Jerusalem if Paul and the other apostles didn't agree. How would we know who to believe then? I'm glad it didn't happen!