Loose rivets
strictly you wold not be licenced to use it, for as you say - its only a one-user pack. The idea is you have one copy on your PC, one on your laptop, one on your notebook, but at any one time you would only ever be likely to use one at a time..
In reality there is no technical reason to stop you using it on far sides of the Atlantic simultaneously. I can't say more without breaching this sites TOS
If you need to recover the product key because you can't find the cert of authenticity key, Google "magical jelly bean"