...a slight variance in the props used (assuming the same exact prop wasn't used), or a problem in the precision of the thrust stand/tachometer. It would have to be a very controlled test environment to gain accurate results.

The area 51 and Da, with vess prop werent the only things tested at a given RPM...sounds like the entire plane could be placed in this thrust measuring device, which opens up even further possibility for differences in measurement. This test wasn't particularly useful, other than resolving that the Area 51 and DA could spin the same prop at the same rpm.