Hi Mary,
That's very odd about the fantasy baptism because the IGI has them both as "Extracted birth or christening record for the locality listed in the record" - not a Church member's entry which were often wrong, but ones transcribed from the parish register. The missing one could possibly be an entry added later in the wrong section of the film? If the unfound one was in Ramsey, that film is a real muddle to view with alternate pages or sections upsidedown, and sometimes in the wrong order.
As well as the two Maughold bapts, Cath in Andreas, and the double-John ones, William Kerruish and Ann Cormode appear to have had another two children bapt Andreas - all extracted entries [IGI].
Sue