I think the main difference between 0-62 times might be made up of how much fuel was in the car at the time of the run.
if fuel ways in the region of 1kg/ litre then the difference between a full tank and an empty one is 50kg, and hence, about 0.5 seconds which would account for runs being done in 6.6 (empty tank) and other runs being done in 7.1 (full tank). It would also make a difference to how much the driver weighed. perhaps as little at 65 and as much as 85, which might account for another 0.2 seconds.