That's now how fare bucket inventory systems work at all. They don't reserve a fixed number of seats for each fare bucket and never change them. Analogies to something like events venues (with a fixed number of seats in each seating section), don't work here. There are constantly updating the fare bucket inventory levels on flights based on various metrics and inputs (including both current and historical demand). They can zero out a fare inventory bucket on flights, and then later add back inventory to it even when no one was actually purchased any seats on the flights.