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Just a suggestion, but could you not do something like this:
If the book is an additional format for a catalog entry that's already present, add it as an additional format for that catalog entry.
If the book is a duplicate of an existing format, ask the user if it should overwrite the existing entry with the same format, or create a new catalog entry.
Of course, you know best if there are reasons why this wouldn't work, but it sounds like a reasonable interface.
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