Dave - many thanks for your reply. I'm a bit confused, because "check for updates" says:
You’re up to date!
Evernote 10.65.2 is currently the newest version available.
I don't doubt you are correct about this, but how would anyone know without someone like you?
Second, I am a premium user, apparently since April 2015.
Since posting today, I have been able to delete some other notes without trouble, but others remain problems (so far all in the same notebook). For what it's worth, these are marked as "only you" - they aren't shared with anyone, so I should have full control.