The unitarians in Ephesus were regenerated before their Christian baptism by Paul
The Alexandrian Hebrew Christian Apollos had long been mighty in the Scriptures, fervent in the Spirit, and knowledgeable about the baptism of John — even before he arrived in Ephesus. The indications are that he had already been baptized before reaching Ephesus, but that it was there that he learned the way of God more perfectly. For only thereafter are we told he showed the Jews from the Scriptures that Jesus was the Christ.
Some take this as an indication that his own full conversion to Jesus Christ personally, was only post-baptismal. In that case, the Romish thesis that he was converted by baptism — and the Lutheran thesis that he was converted during baptism — is thereby rendered more doubtful yet.
After Apollos had departed from Ephesus for Corinth, some unitarians arrived in Ephesus who had never even heard as to whether there is a Holy Spirit. Surprisingly, they later told Paul they had previously been baptized "into John's baptism."
The Romish Church and others wrongly take this "John's baptism" to mean the baptism which had been administered by John the baptizer himself. They also wrongly claim that the latter Johannine baptism was not Christian baptism, and that all those baptized with Johannine baptism still needed Christic baptism.
If these claim were correct, they would establish quite clearly that nobody was regenerated during the administration of Johannine baptism. The claims would then also imply the unlikelihood of anyone being regenerated during the somewhat similar Christic baptism (even if a different rite). Yet in point of fact, Johannine baptism is essentially the same as Christic baptism. Consequently, nobody was regenerated — during either Johannine nor Christic baptism.