Multiple AIFF file transfer to new computer

Uh-oh.

iTunes has its own way of doing things. It's kind of like me. Nobody else can make sense of my organization but that doesn't matter, I can and that's what matters. When you add a file to iTunes, iTunes notes the metadata, then it puts the file in a place it wants to and makes note of that location. If you do anything to change that location outside of iTunes the application won't know where it went. Thus "uh-oh" when you say you "cleaned" them up. It reminds me of when my mother "cleaned" my room on rare occasion and I couldn't find things for weeks.

You probably started off misunderstanding this when you "redirected iTunes" to your new location. I bet you did that with preferences. Wrong. Preferences does not tell iTunes where to go to look for added media, it only tells iTunes to store new files in that place. If you are moving a library from drive to drive you need to move the entire iTunes folder intact, then start iTunes while holding down the option/alt key and tell it which library to use.

You can, of course, simply start a fresh library (use the option start method) and add your media files to it. Try putting them in the Automatically Add To iTunes folder so iTunes moves them to the place it wants them (otherwise it copies them and confuses you into thinking it hasn't done anything with the file).

Artwork depends upon how you got it. If you added it manually it should be attached to the file. If you used iTunes to fetch it then iTunes uses a reference copy stored as a completely gibberish code in the Artwork folder and you will have to fetch it all again since the library database won't connect your new entries with it.

Realize when you add the folder to iTunes iTunes will organize your files as it wants to. There are ways to disable this but you then won't be able to use certain features such as find artwork or automatic repairing of broken links.

I may be mistaken but I do not think the old artwork folder is usable. It relates to references set up in the old library. It is like each artwork is give a code number and referred to that number when linked to a track in the specific iTunes library. You will have to fetch artwork again unless some is embedded in your AIFFs.