The Ephesian disciples received an adult (non-Trinitarian) baptism of repentance from John and do not appear to be aware that the One of whom John spoke had even come.
Apollos obviously was not fully instructed ... he only knew of John's baptism, a baptism of repentance, not Christian baptism, but verse 25 reads:
He had been instructed in the way of the Lord. And being fervent in spirit, he spoke and taught accurately the things concerning Jesus, though he knew only the baptism of John.
From what I can see, knew the way of the Lord, and accurately taught about Jesus. The author appears to be going to great lengths to establish that Apollos was a Christian, but had a lack of knowledge of Christian baptism. The "way of the Lord" would clearly imply that Apollos was Christian (even more pointed than Acts 9:2 a "generic" reference to "the way" but clearly implying Christians).
If anything, the passage is showing how the church dealt with error in the teaching of baptism as it went forth from the beginning. The error was thinking that Christian baptism was a baptism of repentance, just as John's baptism was. Teaching of baptism to those that are already Christians is very rare in the Bible. The vast majority of instances of baptism being to those that are being converted from pagan backgrounds; i.e., they do not already believe, and so are instructed to both believe and be baptized. This is not those in the church now and raised within her. To them the instruction is very rare indeed ... and then mostly dealing with other problems, not instruction on baptism itself. We see those few places as baptism is: 1) being dead to sin (Romans 6); 2) being into Christ (1 Cor 1); 2a) is the whole church (including those past) 1 Cor 10 and continued into chap 12; 3) is clothing oneself with Christ (Gal 3:27) 4) is indicative of unity (Eph 4:5); is equivalent of OT circumcision (Col 2:11,12); and 5) is our identification with Jesus (1 Peter 3:13-22). (I don't include 1 Cor 15:29, as I take this to be Paul using a particular practice that he does not endorse to show that the Corinthians did not hold consistent with what they were saying.)
That Apollos knew "the way" is fairly clearly stated, but he did not know Christian baptism. The same appears to be true of the 12 mentioned in chapter 19 ... Paul did not relate the gospel, but upon telling them there was a difference between John's baptism, and Christian baptism, he baptized them into the name of Jesus and they received the Holy Spirit. There was no need to tell them to repent and believe, they already did believe, but had not been baptized. This is in contrast to what we see in Acts 16, where the message had to be told first, then when the response was evident, the converts were baptized. The same model is evident in Acts 18:1-11 (as well as earlier times within the spread of the gospel). Acts 18:24 - 19:8 is the first time Paul (or anyone else for that matter) came upon people that already believed in Jesus, yet had not been baptized into anything other than John's baptism. So what did the church do? It made them aware that there was not only a baptism for pre-Christian era repentance to prepare the way for Jesus, but also a baptism that was into Christ, i.e., an identification with the visible church and Christ. I am convinced these men would have been Christians, they knew the way; they had just not been instructed as to the need for baptism as a sign and seal of the gospel.