Originally Posted by tt7

None at all, as far as I know (at least not in any 'direct' sense). 'A' is also discounted (paid) FC (used for RTW tickets etc.).

If you want to see X inventory, you have to specifically ask for it. There will (in theory) always be as many A fares available as there are X, and as many F as there are A. However, just because F - or A - is available doesn't mean there'll be any X.

One way to get a "picture" of what it's looking like is to (a) see what the tool shows as available (bearing in mind that it'll never show more than F4 A4, even if the cabin is empty) (b) see what ITN says is available and (c) see what the seat map looks like... Taken together, it'll give you a sense of what the likelihood is of X opening up.
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