I transcribed 1718-1793 for Lonan (which is parish in your example film) - www.manxnotebook.com/famhist/pregs/lnbp1718.htm - see my comments there

my understanding is that the iMuseum entries for pre 19th C are basically provided by the mormons (I think some 19th C was local transcriptions but then 'reworked' by the Mormons) - I havn't checked the accuracy (the old IGI was littered with total junk in many places) - the iMuseum is acknowledged as incomplete in several parishes - AFAIK they did not incorporate Bishop's transcripts