Yes I am pretty sure they were ok. I think what I might have done is when I dropped the files into the music folder on the AK240, I inadvertently placed them on top of an existing file and it's then picked up that file's artwork. I'll try your suggestions when I get home tonight. I suppose as a last resort I could delete those files and then re-load them onto the device but that's going to be a pain to do!
I'm pretty sure that when you run Initialize Media Scan, which basically rescans your music files, you'll be OK. I'm only speaking from my past experience. Been there, done that!