Why one cruiser class could carry different aircraft

Could each navy use one standard catapult for all intended aircraft?

Only temporarily; increasing aircraft weight forced catapult upgrades, so ships of the same class could end up with different aircraft limits.

Navies sought common launch systems, but reconnaissance aircraft grew heavier and required new catapult generations. A standard installation therefore remained standard only until aircraft weight exceeded its launch capacity. Upgraded ships could operate newer machines while sister ships with older catapults retained lighter aircraft. The distinction was especially important for light cruisers whose smaller structures favored compact aircraft such as the Fairey Seafox.