vincheckup not showing entire history.

i wanted to look up a vin on a car im interested in buying to look at the car history, so i used vincheckup. the history came up but the last recorded history was when the car had below 500 miles and still was being listed at a dealership. this car has over 20k miles and i see no history of it after it was purchased and sold. why is this? should i be worried?