I could have sworn I previously read a post here that said all fairfight bans / kicks / stat resets would no longer be allowed as evidence. Is this true? If so, when is the cutoff date for allowing them as evidence? 

Thats the closest i found to it: https://bf4db.com/forum/thread/erroneous-fairfight-bans-859

There was a cheater using a self hosted hacked server to spoof player ID's and trigger fairfight suspensions. Because of this we temporarily suspended Fairfight bans. We would consider them as primary evidence again

They can be used as primary evidence. PB violations, on the other hand, can not.