iTunes again

The reason for the query in this post... I've got a weirdie in the Movie library and went looking for any common factor.

It was fine up until yesterday, when I ripped about 10 DVDs of assorted films (MacTheRipper and Handbrake) and imported them. Found the cover graphics, mostly from IMDB, added them and inserted a few more details.

In iTunes everything is fine, but when I access them from the Apple TV the cover graphic doesn't get picked up for anything after a specific timestamp, ie one of the first films I imported.

I've tried deleting (and trashing) entries around the time in question, but when I re-import them it's clear that iTunes hasn't completely removed them; any info I added at the first import (date, genre, comments etc) is still there.

I think I may need to force it to rebuild the database, or at least do a "sanity check", but I can't see how... I'm also open to any other suggestions