Until the Manx Museum embark on a refilming of these early wills you are very unlikely to know if any are missing - I did gain access to the part bundle of 1665 which contains a reply to an undocumented visitation of Bishop Barrow which tho microfilmed was not that readable but the bundle was not suitable for much handling - some conservation work is needed - you need only look at earlier films to realise that much more conservation is needed for these tho new digital filming would greatly improve readability but this is very unlikely to take place for some years.
I understand that 18th C wills may be the next major task but that after the digitisation of 19th C ones has been completed.
What may be worthwhile with those with access to LDS films is to look at what might be a missing film to see if it merely duplicates other films.
As for some of the names in BL's index I'm still confused after yet more checking as to where they came from - the earlier episcopal wills c. 1660 are often numbered in a bundle that does have an index tho this bundle contains an odd mix of other documents inc presentments - much of the material relating to Bishop Barrows all too brief stay in Diocese in in these films - he certainly shook things up!