The answer to OP's question is "sort of". B6 uses sophisticated software to predict sales based on a lot of datapoints. Thus, it is not a fixed number of seats at a given price. Rather, the RM/IM software is predictive. For example, if a given flight is typically sold to 45% of capacity at 45 days out, it is likely to sell out before the flight. Thus, B6 should stop selling the cheap seats once it hits 45%. On the other hand, if it does this and there is lousy weather predicted for a leisure destination or the stock market crashes and people don't purchase as expected, B6 can open those seats up again at the cheaper price.
This is not markedly different than any carrier.