difference in ecu numbers ex:#01, #72,ect

[4gotn1]

i just came across another ka24e ecu and i was just wondering what all the numbers ment, and if that was anything majorly different from one to another. is there any where on the internet that can list all the different numbers and what not. i have allready searched for this so please dont flame me. and i checked the faq but didnt find what im looking for.