The two designs are nearly identical, but the 300 bar valve outlet is deliberately deeper so the shorter 200 bar connector will not be long enough to seat properly. This is a safety feature to prevent connecting a low pressure device to a high pressure supply, but it works perfectly well to use a 300 bar connector (like those found on most dive regulators) with a 200 bar valve outlet. The 200 bar outlet can also accept a screw-in adapter to convert the outlet to accept the standard 'yoke' style regulator fittings. It's important to understand that the "200 bar" or "300 bar" descriptions are just slang terms that have nothing to do with the pressure ratings of the outlets and connectors themselves.

For details read SCUBA Valves: Regulator Fittings, 200 vs 300 Bar FAQ and Cylinder Neck Threads.