Unless your are in direct access, numbers do not always reflect true inventory. The airlines update the CRS systems 2-4 times a day and even then, CRS systems can show bogus inventory. There are times when CRS systems will show inventory in a certain class when in fact there are zero seats available.

On the other side of the coin, Airlines will often show zero inventory on routings (with a connection) but the individual flights will show inventory. An example would be American showing zero N seats for a flight from SEA to MSY (connecting in DFW) but the flights from SEA to DFW and DFW to MSY both show N seats available. Yield managment at its best.