"Back channels" are exceptionally rare between HR departments -- I've only heard of one significant network of HR departments willing to back-channel pejorative

"Back channels" are exceptionally rare between HR departments -- I've only heard of one significant network of HR departments willing to back-channel pejorative data about possible employees, and that was a set of industrial companies that had an ongoing problem with employees getting fired for failed drug screens, then cleaning up just long enough to go to the next firm. (Meth heads playing with 2000°F furnaces is a legal and operational nightmare scenario.) Even so, it took years for the companies to start sharing anything, and even then the HR heads would do things like meet in the parking lots of rural truck stops to exchange names of problem employees. Basically, sharing pejorative employee info between companies is something that no competent HR professional is willing to do absent very good reason, executive direction, and a lot of attempts at tradecraft. Having said that, ref checks can communicate quite a lot without communicating anything in particular; pregnant pauses and careful word choice can certainly say a lot. However, this is more a concern in SMBs where the ref check might land on the manager's desk instead of HR. Now, if a company leader wants to screw you over and you're looking for employment in the SMB market, then, yeah, change cities. YPO is a freaking henhouse for gossip, and bad reputations move fast in those circles.