"I am sure you have had someone inform you that although Hap Sharp completed 65 laps, good enough for tenth place, this was the second year that the CSI had their new "classification" rule in effect, meaning that to be "classified as a finisher" in a world championship event that you had to complete 2/3's of the race distance. 

At Watkins Glen, that meant, what, 72 laps? This meant that Sharp fell a few laps short and was not "classified" as a finisher. It was introduced to reduce or eliminate situations where drivers could actually complete more laps than another driver, but if you retired too far away from the pits to push the car over the line, you were listed as being "retired." 

In 1960, Graham Hill lost a third place at Spa because his pit was on the far side of the finishing line, so when it had engine problems and he pitted, by not stopping prior to the finishing line and then creeping across after the winner -- Brabham -- crossed the line, he lost a very nice placing in the race. So, despite finishing enough laps to have gained third, Hill retired from the race as far as the results were concerned. 

 In 1966, it was changed to 90% where it has been since then."