What happened to your backups?. Here are some situations when things may not be available:
Apple Media Services Terms and Conditions - Legal - Apple Media Services - Apple
- "Our Services are available for your use in your country of residence (“Home Country”).
And: "Certain Services and Content available to you in your Home Country may not be available to you when traveling outside of your Home Country."
- " Purchased Content will generally remain available for you to download, redownload, or otherwise access from Apple. Though it is unlikely, subsequent to your purchase, Content may be removed from the Services (for instance, because the provider removed it) and become unavailable for further download or access from Apple. To ensure your ability to continue enjoying Content, we encourage you to download all purchased Content to a device in your possession and to back it up."
I don't know for sure but I believe if something is not showing as having been purchased (and you have only ever had a single account and did not get it via Family Sharing) then it is possible it may have been reissued. For example, a remastered CD. You bought the original, not the remastered one, but maybe the original one was withdrawn when the remastered one was put up? I don't know for sure.