I this has been discussed in detail, but let me lend my limited knowledge.

The number of available seats is usually limited to 9 or 7, depending upon the reservation system, so if you see 9, that could be 9, or it could be 20 or 30.

First Class is usually F, A and sometimes G. F being full-fare, and A discounted. Let's say there are in fact 7 First Class seats available. You might see: F7 A2, which would mean that of the 7 seats, all are available at full-fare, but only 2 at discount. Not all city pairs will be eligible for the discounted fare, but it will show you if a seat is available, i.e. it might be available, but not to you.

Business Class is usually C, J and D. Not sure about the difference between C and J, but D is discounted.

Full-fare coach is Y, and almost full-fare contracted rate is usually B or M -- depending upon carrier. All of the other letters are usually variations of discounted coach.

-- John

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