Brian has given reason I think - up to 1877 B&M are on IGI, post that date (until 1901 when data protection of still living people begins to click in) on readily available Mormon microfilms - the IoMFHS has transcribed most if not all burial regs which until a year or so were all in custody of individual churches (now in Manx Museum) - Brian's index is actually an index to these IoMFHS publications (the purchase of which obviously helps the society)