GTS or GSS

Well this is starting to make some sense to me. A buddy sent me pics 5-6 years ago of a friends 68 dart and swore it was an M code. I told him that only 69 were Mcodes. I was wrong...again.
I cant remember if he sent me a pic of vin or fendertag with the M in it.
Would M be in fendertag for 68 or 69?