Any handicapping system is likely to have wide interpretation from the players, especially when guys think that they're handicapped at a higher level than they'd like.
The A-B-C system is no different. It was used for simplicity's sake. Here locally we added an AA level simply to prevent a genuine touring pro from coming in to steal first place. Most of the players were B's and C's, with a few A's. We've only had a couple of AA's (Nick Vita, Cliff Joyner), and they didn't do very well.
The A category was intended for top area players. By "area" we meant a large region, or several states. So an A player is one who is in the top echelon of players over a wide geographical area, not just one room, or one city. Jerry Brock and Gary Abood were both A's. Mike Surber was an A in our first event.
The better players in any given locale's room might be B's, whereas the average players would be C's.
Doc