I got an EUA e-mail at 9:00am for an 11:00am flight once. I have also gotten upgraded with no e-mail, possibly never having been EUA'ed, but manually upgraded before check-in.

If in doubt you can check your seat assignment on-line to see if you have been moved. A good practice anyway, because CO might have changed plane types from the time you booked (from a 767 2-3-2 seating to a 757 3-3 seating for example) and your assigned seat could become much worse.