If you’ve provided your old details, your UCI will revert to the same old one (8 or 10 digit) once you get AOR. These CANXXXX formats are for EE only.
I doubt it. I got my AOR 10 days ago. It is still CAN000XXXXXXXX. For me as well as wife.
In fact I don't remember this earlier but I just checked my profile again right now. And it seems that now both my daughters also have a UCI assigned to them. I certainly don't remember them being assigned a UCI earlier (I remember me and my wife getting it). They are 3 and 1 years old respectively.
So yeah, it actually hasn't changed back at all.