1. These studies have not been done on players who played after implementation of new safety rules of contact, equipment upgrades, rules for sitting out after concussion, etc...
2. I could be wrong but was there a sample of brains from non-football players? Players of other active sports? I didn't see one. Science usually requires a control group to be widely accepted. Maybe a majority of people have this regardless of football participation. Or maybe it is related to active sports where running is involved jarring the head. Maybe the heat of summer practices causes this. Sounds dumb but who knows unless those groups are also studied. Using only 1 test sample tells you very little.
3. We did not get any results on what percentage of these players ever experienced any symptoms from their injuries. Some people may technically have this disorder but it does not affect their life. More research needs to be done on how common life-altering symptoms result from this type of injury and to what extent these players experienced it.
I believe that there is a likely a correlation to brain injuries from football (at least the old way that it was played), but this study is full of holes that need to be filled with more research and data.