Need help to understand the rom code

[Guest Rommer]

Sorry to boring you guys, but I need your help,

to understand the meaning of the rom code :

Unce upon the time there was 6.1 and 6.5 rom,

and 2 rom codes number.

the newest rom get the bigger number

Now there are at least 4/5 breanch :

28230/21876/23506/23616/23551/24001/28217/28205/23517/23515/28014

some of them are the newest version of a old one,

I suppose 28230 are the newest version of 28217,

but :

What is the newest between the 28* and 235* ?

What are the differences ?

thanks in advance