wyowillys46 is correct the issue is 1981 and newer needing 17 digit vin numbers. Vehicles originally designed and used by the military only have serial numbers and most don't come close to 17 digits in Colorado.
Now the rub is 1981 and newer and the fact the AM General put that letter out that the HMMWV to all the states folks in charge of the DMVs nation wide was never designed to fuction on the state highway system. This letter was written by highly paid lawyers who are looking out for their client interests only. First instead of saying HMMWV it's written as Highly Mobility Multipurpose Wheels Vehicles designed for the U.S. and other Militaries, leading those to think who are reading this letter that it applies to ALL VEHICLES OF MILITARY ORIGIN! Also the date starting production of the Military Hummer was after 1981 so the letter addresses the serial number versus the civilian Hummer having a actual 17 digit vin number and only the Hummer brand with the 17 digit vin can be titled for ON ROAD USE ONLY, the vehicles with serial numbers were never ment to be used on the public highway system by private citizens so these vehicles should only be titled for OFF ROAD USE ONLY.....
You can see how this letter and the interpretation of it has just messed up everything. AM General is happy as a fat cat about it maintains their control of interest. Also with all the other makes of vehicles that been put into the pot with this letter the value of the market goes down because only the scrapers will bid on these auctions and most will end up scrapped.
Now back to the HMMWV and the Hummer. Same running gear, same frame, same body. And just like the modern Jeep you can remove the doors, remove the top,lower the windshield. So what is the difference? Hold on NHSTA requires 3 point seat belts, ok both have that or can be modified. Side impact beams, what about the Jeep and removable doors? Now air bag and padded dash I'll give you that one but that is required manufactured new and the original receiver of the vehicle would know of the non conformance.. now we are not talking new, we are talking used and most used vehicle purchases are assumed as "as is and where is" with any and all defects known or unknown also. So why is it such a big deal?