the duplicate numbering is in 1769 - I've summarised all on Manx Museum RB585 which started mid way thro 1769 book 2 - the dup numbers are mostly book 1 - you can see these in my summaries eg for Onchan but there are a couple of wills on the film that were not in the index.

I'm not sure the allocation of wills to film is always accurate as BL used the years covered by the index to LDS films and wrote this into his database thus if a film starts mid book there are possibly errors However all my work is done on Manx Museum films which apart from the funnies in Episcopal wills when there are two films covering same period (I suspect a duplicate filming) should match the LDS films