[EDIT - I posted this prior to learning that HMMWV's get restamped with new titles and years of manufacture when undergoing some types of maintenance and/or repurposing, and dates of manufacture frequently do not match options and serial numbers]
I have bought and sold a few cars over the years and many of those were collectors items. Making sure that you have a numbers matching vehicle might not be important for value, but it can keep you out of jail.
Investigate to see if the 1989 number comes up stolen. If the vehicle is stolen, get a lawyer and be prepared to immediately surrender the vehicle to the local police. Then you are in a position to sue the seller.
If this is not a stolen vehicle, there would not be much difference in value between a 1998 and a 1989 HMMWV. You would get nowhere.
If you're concerned about getting a legal title, it may be easier to title a vehicle built in 1989 than a vehicle built in 1998. Conceivably, someone at motor vehicle screwed up and reversed the numbers. Numbers are input by disinterested people who hate their jobs. You should contact motor vehicle anonymously through a telephone that is not your own and ask them how to deal with a correction on a vehicle that is being titled to you, where the serial number proves a 1989 year but the title has the digits reversed.
With all due respect, and perhaps being a bit paranoid, I am not sure about stamping 1998 on the data plate until you figure out if a number was reversed, and if that error is easily corrected. Honesty and attention to detail now may prevent problems later. If you stamp numbers and know they are incorrect, and the vehicle checks out to be stolen, you can be held accountable for possession of stolen property with an attempt to conceal.
In one respect I agree with NDT. Don't stress. The vehicle did not substantially change in that period of time.
On the other hand, as someone who has bought and sold a number of cars... you never want to be in a position where you have to explain your actions, especially when your actions may not have been within legal boundaries.
Keep in mind that you're axles most likely will be old style as well as other things. [People like Retired War Horses can tell you what changes occurred between 1989 and 1998. That information is not stuff I know.]
My humble opinion. Your mileage may vary.
T
[EDIT - I posted this prior to learning that HMMWV's get restamped with new titles and years of manufacture when undergoing some types of maintenance and/or repurposing, and dates of manufacture frequently do not match options and serial numbers]
opcorn:
