iTunes Match artwork incorrect

Hi everyone

I'm really trying to like iTunes Match (and overall I think it's a good product); my big gripe is the album artwork. It's not that it's missing (which is the readily available solutions Apple suggests in the support pages) but that the artwork which appears on devices that have iTunes Match switched on is not the one which appears on my iTunes.

To make matters worse, different devices show different album artworks for the same album/song.

For example, on the Apple TV and my iPad 90% is correct (i.e.: it matches what I have on my iTunes) however on my iPhone I have a lot of wrong artwork.

Any ideas would be great, I've already identified hundreds of songs where there was no artwork (coming through on iTunes Match) and I've manually added the artwork I want for each song (I find some solution, in most cases the artwork is now on iTunes Match, in others, it's as per the problem above (i.e.: the artwork is random - the same song and artist but completely different artwork).

Thanks