Why the pressure Class 900 is not mentioned in API 602

[CKchi]

I am new from the valve industry ,I understand API 602 is standard for steel GGC valves with small sizes. it specifies the pressure designations of Class 150, Class 300, Class 600, Class 800 and Class 1500? i am wondering why the Class 900 is not mentioned? As ocassionaly, i have been asked to provide the valve in API 602 but with ANSI 900 (Class 900).

It there any paticular reason why API 602 does not cover Class 900?

 

[KevinNZ]

In small sizes class 900 and class 1500 have the same flange dimensions.