Originally Posted by
skywardhunter

sometimes I don't believe you when you say you work in hospitality...
So on a LHR-JFK they take fares of all the 97 airlines (made up figure, I know it's probably not 97!) that operate that route and work it out from there?
Yes, but remember that on LHR-JFK there are the anti-trust JVs so there are only a few airlines.
Also, some airlines refuse to accept YY fares on some routes - it's only really used these days for two reasons, creating a benchmark for concessionary travel and for routes where a carrier doesn't want to bother generating a fare.
Basically for every route, a carrier decides whether to participate or not.