the usual reason for a double appearance in the baptismal register is that the 1st was a private baptism and the 2nd a reception into the congregation - usually noted as such in the register (some vicars only entered the reception noting as a sidenote a private baptism some time prior) - only if there was doubt re 1st baptism is there a 2nd(eg some Roman Catholic bapts where the 2nd is noted as conditional) - were Wm + Cath baptised on same day ?