After reading your message I re-scanned them and copy pasted more carefully to ensure spaces are kept during the process. Please find the updated ones below. Seems like your theory is still valid.

*30600000K09..TKG....

*30601018K09..TKGKEYC

*30600000K0A02TKGFASTX

*30601015K0A02TKGFASTX (from another TK flight which wasn't there in the first post, I was upgraded to J, also had 15kg of luggage)

*30602018K09..TKG.... (I had two pieces of luggage, one of them was interlined to a TK flight next day and there're high chances it was 18kg, the other piece taken on hold because of crowded cabin or *G perk)

FBAG can be luggage related. Maybe it refers to free baggage allowance? No idea about KEYC and very curious about it.