SCR = Sport Cruiser ~1993 - 2002
SE = Sport Cruiser 2003 - 2009 (I believe it technically stood for 'Sport Express')
Those both designate the Sport Cruiser class. The difference is the year of manufacture.
SY = Sport Yacht (Typically 35 ft and larger)
SR = Sport Runabout (bowrider)
SC = Sport Cuddy
XR = ? I believe that is the Performance Runabout