Windchill uses a per-user licensing model. That means you can legally have no more users registered on the system than you have licenses. There is nothing wrong with having the same user log on from multiple computers/places, as long as they are the one who is actually using the software. These are the legal requirements.
Practically, you don't actually install any licenses for Windchill. It doesn't (currently) have any way of correlating licenses to user accounts. Compliance is very much "on your honor" (until the BSA shows up to audit you).
