Have you done much tweaking of metadata? Is the file naming the same in all the books (e.g. Blackmask Lives, author name - title)?
If you still have the original files on your hard drive and you haven't done much in the way of fixing metadata, perhaps you could just re-import your collection and edit the regular expression used by Calibre for metadata detection to account for the extraneous data.
For example change:
Code:
(?P<author>.+) - (?P<title>.+)
to:
Code:
Blackmask Lives, (?P<author>.+) - (?P<title>.+)