Did you buy an OEM version?
If not, then a full retail copy is fully migratable to the machine of your choice for life, but as long as it is on only one machine at a time.
So far the Upgrade seems to be migratable as well. But it could very well become locked to the underlying OS at some point in the future since the EULA says it replaces the underlying OS, and if the underlying license is OEM then it might not be migratable.
Your case falls somewhere in between since you used an Upgrade to install to formatted metal. MS was cooperating with the workarounds
at first, even giving them out
, but have issued several dire warnings
that they need to be backed up with a qualifying XP/Vista. Maybe this is a first instance of the plan to enforce that?
There is no recognition of uninstall, however unless another key replaces the one that is on that particular MAC/hardware config in MS activation computers, then it requires a robocall to trade a series of numbers that deactivate it on the old machine and activate it on the new one. If you are elevated to a person, that is when they MIGHT ask for your prior qualifying OS, if they are planning to go that route.