Thanks, yes I'd already done that (checked at EN's website). My Mac (i.e., a single device) definitely seems to be being seen as two separate devices according to the listing there.
How can I figure out which "Mac" device EN is actually syncing to? I assume it's the one marked 'Current,' since the other refers to a date 78 months ago, which is presumably when I first created my EN account. I don't know how two identifies for the same device ended up being created. This issue is new to me, never ran across it before.
I also wasn't able to check my EN version number -- that information wasn't available even when I was logged in to my desktop account, because the 'excess devices' error message blocked access to all features, including checking the version number. (Not a smart move, Evernote Team.) I may very well be in the other 'version' category (the older one).