Recovering itunes songs bought years ago under various email addresses

I have been buying Itunes for over 25 years now. Back then, you got an email address assigned by your ISP, which vanished once you moved elsewhere and got a new address. I have so many songs that I can play on my old Itunes Touch, but not on my computer unless I log in under a long extinct address and totally forgotten password. Has Apple ever addressed this problem? They will cheerfully authorize my current computer to play these songs on my new computer if I log in under the old addresses (which they immediately say is an unsupported account).