Very interesting thread, guys with inputs from people who clearly understand the science of revenue management at a network airline.
Remember all this wisdom next time you are checking availability for your own non rev flights on any airline other than your own. Using a site like idDeals.com to check seat availability forecasts always do this on a sector by sector basis as this will give you the closest to the 'actual' result.
In the example of BRU-LHR-JFK, if you are standing by on this route then the number of seats available LHR-JFK on a BRU-JFK query will be different from the seat availability on a GVA-JFK availability that includes the exact same transatlantic flight.
So always best to check BRU-LHR and LHR-JFK separately.