What gospel did Apollos know before Priscilla and Aquila corrected him?
Before correction, Apollos knew only the Gospel of the Kingdom, which Jesus, the twelve, and John the Baptist had preached. That message was repentance, baptism, and believing that Jesus was the Christ. He knew nothing of Paul's Gospel, which the context identifies as the later revelation. Priscilla and Aquila then explained God's way more perfectly.
Les teaches that Apollos came on the scene knowing nothing of Paul's Gospel. He only knew the Gospel of the Kingdom that Jesus, the twelve, and John the Baptist had preached—repentance, baptism, and believing Jesus was the Christ. That was all Apollos knew. Les notes that the four Gospels belong to the Old Testament era, where animal blood was the approach to God, while the blood of Christ is the way to God once the Pauline revelations come. Apollos was a great, magnetic speaker who opened the Old Testament, but he was missing something. Priscilla and Aquila, described as lowly tentmakers, took him aside and expounded the way of God more perfectly. Les admires Apollos because he listened to them.