I think there is a limit to how many different flights ITA will consider in a given query. The narrower the parameters of a given search, the more likely it is to find the cheapest flight with those particular parameters.
I was thinking that too, so I narrowed the search parameters:
From: YYC
To: QVR;HKG
outbound: Aug 29 (on this day only)
return: Sep 11 (on this day only)
Result: finds the $639 fare
[the previous date I was using no longer has this cheap fare]
now, if I merely change ...
To: QVR;HKG or any airport within 75 miles
...it can't find the $639 HKG flight.
Surely there can't be *that* many combinations of airports within 75 miles with only these two cities to search on a single date ?
Now, if I lower it to 50 miles, it can find the deal.
I used to think ITASoftware was giving me a powerful tool to use, but if the extent of it's combination search is two cities with a 50 mile range...damn.