episcopal wills are not numbered - the index on MNB gives the frame number on the Manx Museum film - I've no idea if these films are the same as the Mormon films.
the wills were bundled with modern paper separators giving the approx year - this would appear to be derived from the date of the 1st will in the bundle - you need look at the will to determine the actual date
The Library is closed next week for annual stocktake etc - I'm not back on Island for another 2.5weeks