It's very possible that 'C' inventory appeared briefly but was grabbed before the next EF query. EF doesn't disclose how frequently alerts are checked but does say that the interval decreases (checked more frequently) as the flight time/date approaches, But it's also possible that 'C" inventory never appeared. RM releases 'C" upgrade inventory on their own schedule based on circumstances. There's a waitlist of PNRs desiring 'C' inventory (either using SWU or miles), sorted by status and then by rolling LP. The waitlist is automatically processed by Sabre when certain things happen, including cancellations in business class. It's also periodically processed by an AA mechanism. If RM makes some 'C' available based on, for example, time to departure and lack of change in flight load (e.g., no new business class bookings), the 'C' waitlist is not automatically processed but will be processed by the AA sweep when it next runs. This is the most common situation where an EF alert or manual EF query that runs in that time window between RM making 'C' available and the next AA sweep can see that 'C' became available and someone can call in to grab it, jumping in front of anyone on the waitlist. But if RM made 'C' available because of a change in the flight load, such as several business class cancellations, then Sabre will process the waitlist and 'C" will never have been visible; it was added and consumed instantly,