This just came up for me. I added a DVD and discovered it already existed in my library, but I was pretty thorough in the new entry so a lot of that info wasn't in the existing one. I looked for a menu feature to merge the two, and no dice. This would be just like the address book.app "merge selected cards" feature, where it would combine details unique to each entry and make 'em one.
Add it to the list! But definitely keep box set nesting in the #1 slot...
Merge Entries
Re: Merge Entries
A merge option is already on our list but thanks for adding your vote.
Re: Merge Entries
Please add my "yes" vote, too.