The BT's are usually derived from the Parish Reg (and I've seen transcription errors in the BT tho sometimes additional info is there esp for illeg births where the father's name may have become known post baptism) - the Gen Reg Office uses the official transcription(generally very good) of the parish reg done c. 1911 - this transcription is on mormon microfilm and can be checked - the original parish reg should now be in the Manx museum and will be produced if you show good reason to suspect an entry in the official transcript.