Howdy Bear,
This can get real deep

I will give you a brief look at things. The US miltary have Mogs that are called SEE tractors (I forget what SEE stands for). The Mogs are mostly construction and utlity vehicles (backhoes, forklifts, front buckets and the like). As far as the Mogs in private hands in the US it's mostly ex military. A lot of what is here is governed by custums. The vehicle must be 25 years old.(that's the simple answer). So the vehicle that qualifies is the 404. As the militaries in Europe get rid of the older vehicles they end up getting sold in auctions and some end up in the US. With production number of 60,000 of the 404 and most of that in the 1960s those are the ones being retired. The contries that had large quantities are; Germany, France, Belgium & Switzerland. There are Mogs that were imported and sold by Case Tractor as utility vehicles that have gone into the private sector and those are the 406/416 which are becoming very popular with Moggers. I will have another post about the Pinz. It won't be as long