The x and y indicate year of manufacture - IIRC, X is 1999 and Y is 2000, it then went K1 for 2001, K2 for 2002 etc.
Mostly the differences in years were minor or colour schemes only. Someone with a Haynes manual will be able to check the X/Y differences if you ask nicely

! I have only got a Haynes for my CBR....
Welcome to the site by the way, I suppose I'd better say welcome to the madhouse too (there should be a smiley for that)