Thomas: How can you consider an out of turn action covered by Accepted Action?
Because a bet was made and called. The action is accepted. The same as in Pot Limit cash games: An over-bet was made and was called. Action is accepted.
I liken it to this scenario that happened in the 10k Stud 8 tournament:
Player A (Seat 3) Late Registrant just arrives to the table and is the bring-in first hand. Betting is 100-200 with a 50 bring-in. Player A puts in 200. Player B puts in 200. The Dealer says Raise, Player A puts in 100 more (300), Dealer says Raise, Player B objects, floor is called. Player B says that Player A bet 200, I called 200.
The floor in this case allowed the raises.
However, it was decided after more discussion amongst ourselves that the better ruling would be Accepted Action. Bet and Called.
So back to our NLH scenario here we have Non-Action by Player A, then a Bet of 500 by Player B and then Player A throws in a 500 chip to call. Under Accepted Action that's a Bet and Call. Action is accepted. Next hand.
This eliminates any further ambiguities.
As Dave Lamb would say, you always rule in favor of the lessor. Meaning less damage to any player. So in this case, that means enforcing the 500 bet and call. Not allowing, the bet to be retracted and giving Player A all his options back or worse forcing Player A to leave the 500 in and giving Player B all his options because "Action Changed". Some rules super-cede other rules and in this case Accepted Action is the better ruling.