If a company has more than one site, there are a few different solutions to prevent problems with the VLAN
The Company has a strict standard and every site has the same VLAN for the same things. In this case it doesn't matter which site you are from, you won't have a problem with the VLAN
If different VLANs are used on the sites, it gets checked if the MAC-Address is known and if the site is another. If that is the case, the VLAN gets set to a VLAN that the site they are currently at needs.
Or the last solution if someone moves to another site his entry in the database gets changed.