An-24B and Xian Y-7 maintanence Categories

I know all these models are not popular used, but is there any reason An24B has a different category from Y-7 and MA60? An24 is now 32, while Y7 and MA60 are 72. i thought Y-7 is more like an An-24RV

Thanks in advance

The Y-7 and the MA-60 are all relatively new Chinese developments of the AN-24B. I think that because the Chinese have modernized the AN-24B so heavily, it no longer shares the same type rating with the Y-7 and the MA-60.

B747s are all under one category. Comparing 747-8 with 747-100, i don't think it has fewer modernization parts than upgrading An 24 to Y-7, maybe even more changes. It's also the same case for B737s. 

Any response from the team?