I thought I'd share my experience / problem, which was solved when I called Apple Support.
I have songs in iTunes purchased under an old Apple ID about 11 years ago. I created a new Apple ID about 10 years ago, and have been using that to purchase songs, apps, etc. I've always been able to play the songs purchased under the old ID until now; when I tried to play songs purchased under the old ID, it would ask for a password. I tried to rest the password, using the email method (and never got the reset email) and then with the security question method (and it didn't recognize my DOB). Then I called Apple Support.
The Apple Support rep tried to verify the existence of my old Apple ID, and couldn't find it in his system. He then checked with someone in iTunes Support, and they told him that at some point, my old Apple ID had been changed to another ID.
Years ago, Apple used to let users actually change the primary email address associated with an ID, which is apparently what I'd done. The problem was that my songs in iTunes were still associated with the original email address I used when I first created my old Apple ID. I reset the password for my old Apple ID (using the email address I had changed it to), went back to iTunes, tried to play a song associated with that older ID, and when it asked for a password, I used the "new" old ID (email address) and newly reset password... and the songs played!