How to quickly stitch a ton of albums back together into compilations?
I've had to fix some music before manually to get them sorted into full albums. You CAN select multiple files at once and change them in one click; if I recall correctly iTunes may prompt you to confirm that you really want to mass-edit files it thinks should not be treated as a single album.

Be careful you don't overwrite anything except the field you intend to change, as you can easily accidentally rename or assign the same artist for all of them at once. To be safe, it might be best to group-select items from the same compilation only.