I can’t answer for all OTA’s, at Future.Travel we have access to many GDS systems. The systems have hundreds of millions of flight combinations available to be drawn out given the correct programming.

We limit the system to the top 300 fastest choices, and then sort them by price, number of connections, and time of day.

What you will see is the fastest responding, lowest priced airfare available for a desired itinerary. We sort out long connections, flights with six or more connections to reach a destination.