I know what Fare codes are and what J, F, Y mean. I was a reservations agent at AA. I was just trying to illustrate the differences in pricing for each cabin using the abbrievated letters representing the cabins. Nothing to do with Fare codes.

My bad regarding M class, your right O class is the cheapest available. I got confused thinking about another airline.

I used Y, Y+, J and F so that so people understand the cabins the fares represent. Airlines, depending on their branding, call the cabins differently.

BA uses World Traveller while Virgin call it economy.
BA uses Club while Virgin call it Upper Class.

I was just trying to use the codes that make sense to everyone. Apart from real nerds, most people assume Y means Economy, Y+ means Economy+, J means Business class, F means First Class. I think you made a mountain out of molehill here!