Computer problem
1991 Cadillac Brougham V8 Two Wheel Drive Automatic 66,000 miles

hi,, i bought this car friday, the milage on it was 66,000,,i started the car up on sat , today .
and the milage went up to 99.000 miles,
on the door it was last inspected in june was 58,000 miles ..what happen? I purchased the car to resale,, now what I have on the title r milage 66,000 , now if i was to sale it they would say how did you put 30.000 miles on this car in a few months, and how would i explain this