I’m not knowledgeable about odometers at all, but if it’s as easy as “hooking up to a computer” to get the real mileage, why don’t people do that when they buy the trucks?
I use my $20 eBay OBD2 all the time on my Mk4 Jetta to confirm faults. However, even with such an old car with decent support, there are many things I'm unable to do or see.