https://www.afkl.biz/trade/s/resourc..._US&country=US

As of a few months ago (when AFKL restructured their fare bases), whether a fare is light/standard/flex is encoded in position 7.

Example:
OGS8THRA is Light, as is ZGS8THRA
OGS8TJJA is Standard, as is ZGS8TJJA
OGS8TMKA is Flex, as is ZGS8TMKA

So to a first approximation, 7th character of R is light, J is Standard, and K is Flex

Every one of those is a promo fare, so position 6 doesn't necessarily have a fixed meaning.