The original discs for all my collection of over 500 CDs are stored in eight boxes in my basement, so when I need one I have to search. Years ago I began using labels on the spine of each case to assign a reference number. My current labeling project is to update the DiscNumber tag field with my own unique number so I can easily find the original disc. This field in available data seems to be infrequently loaded, so this will be a good use of it. This leads me to another idea that I will throw out for discussion regarding downloading tag data.
I am not sure if a scheme where you have 1 id per CD case would really comply with the original idea of the field DISCNUMBER.
But then again: who cares?
What I would like to point out is that you may have to think of a way to separate the tracks of the different cds. Otherwise you end up with several track number 1s, 2s and so on.
True, some cases contain more than one disc. Other collections may be in boxes of up to a dozen or more. I should have been more specific, I number each disc with a marker, and multiple-disc cases get multiple numbered labels, one for each disc. So far this is working well for my library and I can go to a specific disc quickly. Storage boxes will be labeled with the range of actual disc numbers they contain. I'll also store odd-sized collection boxes as a group. Some have boxes the size of 33 1/3 platters, others are variously shaped and sized.
The good news is that so far out of 100 CDs, I've only found one missing track. Not bad for years of maintaining digital copies. Can't remember when I started using MP3Tag, but it is a great tool.
One problem with all the player software I seem to have used is that when using 'Shuffle', which I usually like to do, they will also shuffle the tracks of classical recordings which typically contain a number of tracks. My next project may be to merge the tracks for these into single files unless any of you have a better solution. Haven't searched for that yet but it would be nice to hear the complete composition in track order in those situations. Same for musicals where you would like to hear the tracks in the proper sequence for the story line, and usually hear all the tracks for the show together.