What submergible depth are you referring to? Theoretical, test, operational? When it comes to operational-test depth it depend on more than just the pressure hull material but also pumps,seal, connections. Change of material affects theoretical depth but does little effect on operational depth.
Not all navies also perform or care to test the test depth, they stick by operational depth in sea trials and continue with it. Type 214 has test depth of 400 meters (doubting if tested that far but likely certified for that) but doubting if it would operate below 250 meters. While mentioned test depth of Type 212 (referring to wikipedia as being the mere source of this claim) should be the operational depth. Its test depth should be somewhere between 300 to 400 meters. Theoretical depth (crush depth) of the platforms change by a certain percentage, hence the pressure hull diameter.
