Yes, 9 or more. The reason for this is to keep down computer space, so 9 is the highest single digit!
Normally you'll get the main compartment F, then sub-class A. Then J compartment, followed by C D and I, then Y, followed by a variety of chars, but normally B, H ,K, M, L, S, V, etc. Naturally, the sub class availability will never exceed the compartment figure. Some class figures are specific to that class, where other classes relate to similar lower yield classes, so you could see S8
, and if one more seat was sold in one class it would affect the other - S7
would also reflect V7, for example.
Each of these 'classes' represent a different fare, and space is controlled on what Yield Management choose in their inventory control of each flight, based on past experience together with holidays, and occasional events, like the Olympic Games, where the airline can charge more if they want to.
On top of all this, and other vagaries, these availabilities may differ depending on where they are being viewed. G may appear on a LHRLOS flight viewed in GB
, and N might appear on a LOSLHR viewed in LOS. Reason for this is that directional fares exist on these routings which can only be sold in the country of origin . . . it is all very complex . . . and doubtless improved a lot since my days in the old 'Space Control'!
Per Ardua ad Astra! ........ Honi Soit Qui Mal y Pense!