There is only one gospel. If only Paul preached it then Jesus and the others didn’t preach the one gospel.
A person can only share what they know to share..
So, if a person does not know the Gospel, . then they can't teach it, or preach it.
In Acts 2, Peter, was preaching a water and repentance OT JEWISH concept that is the same that John the Baptist preaches to JEWS.. before Jesus started His Ministry to the JEWS.
Later, after the Old Covenant was ended by the Blood of Jesus, that is the New Covenant, then there was a transition period.. .and that started in the Bible, with the Cross of Christ.
And we when we study the NT, we see that Peter in the beginning of the Acts of the Apostles, didnt have Paul's Gospel, and didnt understand that Gentiles could be saved, and yet, he had entered the "Time of the Gentiles"..
So, it took some years, after The Cross was Raised, and After Paul was called to be the "apostle to the gentiles"... before all the Apostles were all preaching Paul's Gospel.
By Acts 15, they all had it.