Maybe this explanation will help:
You can load the City Navigator/City Select Software to as many computers as you want. 1, 2, 10, 100 computers -- it doesn't matter. You enter the unlock code on each computer that you install the software. The unlock code, however, is not to unlock the software, it is the key to your handheld unit.
So, when you want to upload a map you plug your handheld into the computer. If there is an unlock code for that handheld entered into the computer, you can download maps all day long into your handheld. You can upload waypoints, tracks, routes, into the computer as well.
If there is no unlock key for the handheld unit entered on that computer, then you can't do anything. No uploads, no downloads. You are SOL.
PS: there is no confirm through Garmin's website. You can use the website to "restore" the unlock code, but you do not have to be connected to the internet to be able to use your handheld on on any computer (laptop, desktop, etc.).
Hopefully that helps.