Welcome to the site !!
When you say the "piston is dead" , can you elaborate please ?? , did it lose compression ?? , did a valve poke a hole in it ?? , did it seize up ?? , is it blowing oil out the exhaust ??
According to what i see in the Honda Parts Fiche , they each have different part # , but it does not signify what changes were made , Ken (the owner) would know for sure , but my Factory Honda Service Manual covers from 04-09 CRF250R , , and the only difference i see mentioned is the Top Ring Marking differs , it goes 04-07 , then After 07 , same goes for Ring End Gap , it lists 04-05 then a different gap for After 05 , then Piston Ring to Groove Clearance is one size from 04-07 , then another size for After 07 , what significance that has as far as actual cross fitment , i can't say for sure , but it does list differences , the only thing i could say , is take a digital Micrometer and measure each and see if there is any physical differences , other than that , i would guess that as long as the rings match the piston i would think it would cross fit between those years you have , again to be 100% sure i would PM (Private Message) Ken the owner here
https://www.crfsonly.com/forum/memberli ... rofile&u=3
go to where it says "PM:Send private message
" and click on the words private message
These are the Honda Part #: :::NOTE:::
The Parts Fiche lists a Piston A and a Piston B for 2007 , so i don't know what significance that has either , so its saying for 07 there are 2 different pistons
13101-KRN-850 PISTON 61.99
13110-KSK-730 PISTON A 76.99
13120-KSK-730 PISTON B 76.99
13101-KRN-A10 PISTON 71.99