You're very welcome.
Conditional searches like I suggested above means calibre will remove a book from display when you enter anything into the secondseries column. After all, once there is something in secondseries that title no longer meets your search criteria.
So if you see something else that needs editing, do that first. Then correct for the missing secondseries info. Otherwise you'll lose track of it.
Only other things I would suggest is to run the Find Duplicates and Quality Check plugins. They're invaluable for spotting minor errors. Depending on just how much, and how accurate, you want your metadata to be.