I discussed this aspect of Paul’s polemic some years ago in “Paul’s ‘Autobiographical’ Statements in Galatians 1–2, ” Journal of Biblical Literature (JBL) 85 (1966), pp. 335–343. There are, of course, also problems with trying to reconcile the chronology of Paul’s life given in Acts with Paul’s own statements, but that issue does not concern us here. Furthermore, Paul never mentions God-fearers or God-worshipers, those gentiles who, in Acts, attend synagogues but do not convert to Judaism, and who often are the gentiles who become Christians.