[Sabardeyn]

Hitch,
Another thing that might help when adding books is the merge settings, which should merge ebook formats where the title and author of a newly added book matches an existing entry in the database. Under BetterRed's image above, the last entry Control the adding of books has the settings that you need to control this function. The title and author information is obtained from your current import regex formula (Prefs>Adding Books>Regex) and metadata from filename/inside file settings.

One thing to keep in mind when Merging books is to pay particular attention to the other metadata - pub date, IDs (isbn, asin, etc), cover image, language, and anything else not in the filename. It is very easy to merge two different editions of a book if the title or series doesn't adequately specify any difference between editions. This becomes particularly true if you download metadata (which is prone to errors), get metadata from inside the ebook file, or share a database with another user (do they enter accurate metadata). Or any other variation in contents that would require a new ISBN be issued (guest foreward/intro, expanded storyline, reprint, illustrated, etc).

I'm not sure the above consideration pertains to your usage Hitch, but thought I would mention it -- "full disclosure" and all that.

I hope this is of some help.