So do I have this right?
AC publishes a list of fare codes, which we can view through EF etc., and then the prices don't deviate from that list i.e. prices only move according to those rules (days to departure, booking class).

Fares don't actually change for each booking code, but their availability affects what the price is?
(And AC can withdraw - zero out - any booking class they want, like is their habit when they have seat sales)

Or do prices for a particular fare code vary by day/hour according to their marketing dept?