Before trucks started being apportioned through the International Registration Plan in the 1970s, many required a license plate for every state they drove through. Even though this is mostly not an issue nowadays, Alaska, Hawaii, the three Canadian territories, and Mexico still require commercial vehicles to get a completely different plate in order to drive there.
Many trucks in the northwest have three different plates, and all of them are needed to travel in Alaska, Yukon, and the IRP zone:
I would imagine there are a few that have four different license plates if they are required to travel to the Northwest Territories, too. But I couldn't imagine seeing a truck with any more than that, unless that truck is needed for a very specific route through the US, Canada, and Mexico.
