I mean, the MSA-purchased version is a retail key, but it doesn't give you a unique activation key and seems to use a generic one (at least when doing upgrades), so... trying to move this "retail" copy is really, really hard and inconsistent compared to a version you have a key for.
So, I will admit that it is possible. It's just really hit-or-miss and complicated, which can easily be avoided by just buying a retail package from somewhere with a code inside.