iCloud Confusing situation with two iCloud accounts

[Internaut]

Firstly, Merry Christmas to anyone who reads this today. Now, I have a slightly confusing situation involving two iCloud accounts. I will describe these as:

• In effect the iTunes ID set up in the very early naughties, using my AOL email address, back when having an ISP email address was still a little bit fashionable.
• To this day, this is the ID I use to actually sign into all my Apple devices and is associated with all my Apple purchased content and iCloud storage space.
• Then there's the thing that started out as "MobileMe" (ugh) and, because I "purchased" it alongside my first MacBook, very soon after MobileMe became a thing, I have a valuable <firstnamelastname>@me.com address.
• I'm signed into the Me address with Mail, but not signed in at the device level on any device (i.e. that is not the ID I log on with).

It became painfully obvious, this week, that though they coexist on the same devices, these two accounts don't know about each other. So, when I attempted to reset the forgotten password of my me.com address, none of my Apple received a notification. I assume this is because the actual devices themselves are not signed into this account. This involved a lot of confusion including Apple telling me "We'll take a few days to evaluate your information".

On this occasion, I got lucky. Mail is signed into Me on my iPad Pro and although I don't remember the old password, I was allowed to simply change it (just a few minutes ago, in fact). Now, from my own research I see there seems to be no way to merge these two accounts which is a pity since I suspect AOL email addresses are, generally speaking, not long for this world. So I'm wondering if there's any way to at least associate the accounts more closely?