Well, I just added the functionality for the parent rom to be mentioned on a game info page (
http://www.emuparadise.me/News/comments.php?id=1082). I found that MAME can output all the 'brothers' of a file/driver so it was easy to fill it into the database.
Yeah the CHDs are not so many in number so I think even based on missing files/different files it's possible to find out which ones are new or updated. However, adding them can be a pain because I believe even some file names have been manipulated in the middle.