It has been 25 years since the crucifixion. Apollos had apparently heard the preaching of John the Baptist regarding "The Lamb of God Who Takes Away the Sins of the World." But he apparently left prior to the death, burial, and resurrection of Christ. So he was preaching an incomplete Gospel. His "disciples" believed an incomplete Gospel (1 Cor 15). An incomplete Gospel does not save, and thus their baptism was invalid. Neither was Apollos ordained by any church to perform valid NT church baptism.They were Ot saints, living during the transition into the NT reality.
Those "disciples" heard the Gospel, believed, and submitted to baptism.