Well about the only logic you CAN apply to it...and yes I know this is not backed up by anything, so don't kill me.
LE = Luxury Edition
SE = Sport Edition
SLE = Sport Luxury Edition
SSE = Super Sport Edition (Think about it...SS on cars used to mean Super Sport, why would it not apply here?)
SSEi = Super Sport Editon Inducted
Disclaimer: This is only my logic, no one has to listen to me!