Tip: I have been doing the upgrades for most customers with their old unlock keys. This has been working and gets me away from worrying if Sage have generated proper new keys.
One area that I found is a ""gotcha"" (at least I think the keys are part of it) is if you are using the BOI interface with Starship.
Under the older (4.2 and below) versions I believe the BOI was a separate key on the MAS90 registration screen.
In 4.5 BOI is integrated to the overall keys -- so if you just use the 4.2 (or early) keys you won't be unlocking BOI (because 4.2 used a separate BOI key and there's no place in 4.5 to enter that).
In my case the Sage posted keys did not seem to work either so I had to call and have Sage re-generate them (which is what I expected).
Just an FYI