c 1911 all parish regs were called in by Gov and transcribed (in lieu of absence of civil reg pre 1878) - these transcriptions are the ones filmed by mormons and still offered as the parish regs to users at Manx Museum (there are however a very accurate transcription when checked against the actual parish regs which may eventually appear as digital images at iMuseum) - the IoMFHSoc used I think the original parish registers as the basis for their transcribed burial regs - they were however considerably less accurate than the 1911 transcription especially for the early years - Lawson then reindexed these IoMFHSoc transcriptions adding his own errors (typically between 2 to 10% of entries depending on parish)
Hope this helps