Licensing question, after upgrading

I've read the tutorial where you can effectively use a Windows Upgrade product as if it were a full installation, thereby omitting the need for a previous Windows operating system to be installed. The reason being that the upgrade has its own unique licensing number, rather than requiring the license number of the upgraded operating system.

But, what happens to the original operating system license if you upgrade it? Here's the scenario I have in mind:

• You have a full retail license version of Windows Vista Ultimate installed
• You successfully apply the Windows 8 upgrade to your installation, which now has an updated license number.
• You have another computer running Vista Basic and wish to run Vista Ultimate on it.
• Can you technically install Windows Vista Ultimate on the second computer? Or, does Microsoft log the Vista Ultimate license number as having been "upgraded to Windows 8" and as a result prevents activation?

all i know is i keep using some of mine[retail] on the same pc after ever install

The base license used for an upgrade is subsumed into the upgrade, and CANNOT be used elsewhere, legally.

^ Well technically an upgrade should not be used without a previous OS installed, yet it is well documented (unofficially) that you can do this. Whether you upgrade an existing OS or do a fresh install without a prior OS, the product license number remains the same. Isn't that right?

The reason why I bring this up is that I'm planning to upgrade my OS but on a new drive. I'll keep the original drive in reserve, to use in case of a fault or issue with the new drive. I just want to be sure that it will still function properly.

There's no 'technical' problem - but there is a huge legal problem!
read the upgrade terms which you agree to when you install the OS.

15. UPGRADES. To use upgrade software, you must first be licensed for the software that is eligible for
the upgrade. Upon upgrade, this agreement takes the place of the agreement for the software you
upgraded from. After you upgrade, you may no longer use the software you upgraded from.

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