Embedded artwork not showing up

Sorry guys if this has been asked before. I had a major virus and had to wipe out my computer. Long before this happened, I had all my music backed up on an external drive, and also 2 copies of all my files burned onto data disc directly out of iTunes.

So once my computer was up and running I downloaded the latest version of iTunes. So my next step was to start loading the stuff I needed back into iTunes so I"m ready to load up my iPod when I need to. So Since everything is more organized on my data discs I decided to load up my music back into iTunes from the data discs rather than from the external drive. When I did this I noticed some of my embedded artwork showed up and some didn't. I'd say about 30% of my stuff had artwork from the iTunes store so I understand that that isn't going to show up since it wasn't embedded. If you're artwork is embedded, shouldn't it hold all your artwork in the files even after you burn them to data disc? Does it make a difference that I"m using a different version of iTunes then I was when I embedded everything?