What's the difference between Bumptracker and the data airlines keep?

Airlines do record bumps and the compensation they give out and base their decision to oversell future flights on this data as well as other variables.

Bumptracker merely allows one to see this data in a reported form and make an educated guess as to what flights might possibly be oversold.

In any case, logging your bumps on bumptracker doesn't affect an airline's descision as to which flights to oversell since they already know each and every oversold flight.