But that aside, why does Opera 12.16 not find an update when I tell it to check for updates?
If you are using Opera for Windows (what i think you are based on the forum where this topic was created) then it should have found 12.17 as an update.
Opera Presto will not upgrade to Opera Blink because the last is considered a new product and not and upgrade. Maybe it may change in the future but only time will tell.