{date} does not show in Bulk mode because that would apply to all selected.
Timestamp will remain on a merge (at destination), so the direction of a merge is important.
If you use
Find Duplicates: Sort the results on 'Date' column, them select the top one FIRST (the first selected is the destination)as part of the Merge. (assumes sort arrow low.High)
You DO have to do this Book by Book. But it does not take that much time
per book.
(And it will remind you to never let things get that out of whack in the future
)