I worked in a building that sealed one staircase shut if a fire alarm was pulled because it accessed sensitive areas. It was meant to get to them and if you were in it you could escape but it was useless for the rest of the building so you’re right. Just because it’s a stairwell doesn’t mean it counts in an emergency

Well here stairways also need to be usable in case of emergency, especially fire. Everything has fire codes that must be observed, we frigging don't call a stairway an emergency stairway just because it's legal. AFAIK even if you have 3, they ALL need to be according to safety protocols.
Also AFAIK we need to have at least 2 "emergency" stairways already above 2 floors.