If you're talking about Apple Music Match (think that's what it is called), they don't really upload your MP3's and replay them like they used to. I "ripped" all my CDs years ago for that and for most of the CDs, they would essentially fingerprint the songs that you uploaded and match it to the track in their system. If it wasn't in their system, the track went off to storage and you could get it there. Over time, iCloud and streaming have taken over. If Apple doesn't have the streaming rights for a particular song, it disappears from your music match. We noticed it mostly from my wife's favorite Christmas music CDs that we ripped and have long since been discarded. One CD in particular keeps losing tracks over time. So, if you pay for Apple Music and have Music Match, it's pretty much a waste of money. Similarly, U2's Rattle and Hum was one of my favorite movies from the 80's. But you can't find it on streaming anywhere supposedly because getting the streaming rights for all the songs would never happen or be too expensive when you need licensing from that many sources.