You can check when you are making a steal.
You can check to see what position you're in.
You can check to see if you made the first raise.
Therefore you can build a stat for how often someone did not make a steal, and then got 3-bet when they were not a blind.
You cannot tell when you are on the button that a raise came from any specific position with 100% accuracy. If either blind gets involved, you lose that data. We only store position data on one opponent: whichever opponent was the last opponent to raise. Yes we can therefore pick out the situations where the CO opens, the BTN 3-bets and the CO folds from both directions. What we can't pick out are the opportunities. Specifically we can't figure out how often the button had the chance to 3-bet in that scenario because there are some opportunities where he opted not to 3-bet that will get lost because one of the blinds will 3-bet. Since we can't get an accurate opportunities column, we can't get an accurate stat. A specific stat for "fold to 3b from CO vs BTN" is not what the linked thread talked about at all. It talks about how often a player 3-bet facing any raise so long as that raise was not a blind steal. If you wanted any button 3-bet, that we can do easily. What we cannot do is button 3-bets vs exactly one particular position.
I hope that clarifies things a little.
