I guess it’s always possible that they’re making stuff up on the fly.
I did a google search for Privacy Badger review and Privacy Badger test results but couldn’t find any good independent tests. I was hoping to find something akin to AV tests where they might load up a webpage with trackers and such then report on what gets blocked. No such luck.
I guess you have to consider the source when evaluating whether they’re being honest or not. I trust EFF not to lie to my face and considering Privacy Badger is free and not ad supported I can’t see any reason for them to be dishonest so I assume it’s doing the best job it can.
It would be nice to see serious, independent, test results though.