Incase anyone sees this thread, my issue and resolution was this (Call to apple support took care of it):
I had a really old appleID, from the 1990s when it was still itools. These older IDs were username/password, not email address/password. I've had my email address since .mac service started (many years ago). At some point when my older account was upgraded, my current email address was added as a verified address on my appleId. At some point later, perhaps because of a phone purchase or something, a *new* appleID got created which used my full email as my account name (not just the first half). This account also had my email address as verified. Due to some service change, I was required to update my email verification for my new account (the one I use every day, the one that I didn't realize was any different than my original account). However, when I tried to do that, the system saw my email as already belonging to another account (my ooooollllllddddd one).
The solution was to gain access to my old account (the one with just a username) and remove my email from that account. Then my newer account started working on its own.
Old account:
myUsername, verified email: myUsername@mac.com
New account
myUsername@mac.com, verified email: myUsername@mac.com
I wasn't aware these were two different accounts, the old one hadn't been accessed in years. Switching my old account over to a gmail address, it freed my main @mac email address for use with my new account. I don't know why this didn't happen before I ran into this issue this week.