Why there are different gasket kits for evo8?

I see that they are different:
OEM MITSUBISHI ENGINE GASKET KIT EVO 8 12/02 - 6/03
OEM MITSUBISHI ENGINE GASKET KIT EVO 8 7/03 - 7/04
OEM MITSUBISHI ENGINE GASKET KIT EVO 8 8/04 - 7/05
OEM MITSUBISHI ENGINE GASKET KIT EVO 9 8/05 - 11/06

why is it so?

How can I understand which one do i need?

I have evo8 engine in my evo4.

 

That is a good question. Those look like dates to me....

 

those are dates for sure, but fine - how can i guess which engine i have? or there is no difference and i just can buy any of those

 

any ideas?

 

If it is the original engine, check the build date on the door post.

 

Well, my car is evo4, however my engine is evo8