In the past couple of years I've stopped and looked at 3 mid to late 80s Cabrios, and all three had 60-70 something thousand miles on the odometer. I didn't talk to anyone about any of them, just saw them for sale and stopped. The odometers on the ones I looked at would register up to 999,999 miles, and still showed a 0 in the 100,000s place . . . all three also appeared to have well over the milage that was showing. This one sounds like it fits the same profile.
I would bet that the odometers on these things typically break between 60 and 80 thousand miles, and that if I had checked the odometers on the ones I've looked at were no longer racking up miles. Did this one work?