What's the exact definition of alpha 500 - a "run of 500 meters" with a jibe, or a run of "500 meters or less"? It seems that GPS Action Replay uses the first definition (which is from the rules on this site), and GPSResults uses the second definition (which is from the rules for the GPSTC site). 

Most days, there will be no difference, but sometimes,the difference can be quite dramatic (see http://boardsurfr.blogspot.com/2016/12/never-trust-software.html).

It is any distance 'up to' 500m. I was under the impression GPSAR used that definition like everyone else. It may be just that particular session file ?

I just checked two additional files, and in both, GPSResults finds alphas that are substantially shorter than 500 m (e.g.428.5 m), while GPSAR gives slower speeds for a distance much closer to 500 m (e.g. 489.2 m). I can't figure out how to post images here, so I'll post the screen shots on Seabreeze.