in general...just between korea and china...
korea serials have just 1-letter...china serials have 2-letters...
in the case of I (Saien / Shine)...they opened a China plant IIRC in 2002.
some say that China plant also makes Epiphones, with the I serial too.
when they started producing Epiphones? no idea cos only gibson knows.
so the best way is to email gibson customer service with your serial, and they might know whether your I serial is china or korea.