Why can't I find certain flights in the Connections API?

You will occasionally find flights in the Schedules API but not in the Connections API (or vice versa) as they use different algorithms. Please also note that the Connections API provides access to information on upcoming connecting flights with up to three stops from today forward for up to approximately 90 days. Anything beyond this date range, you are unlikely to find a matching connection.

Results from the Connections API may vary because each flight is scored and displayed based how well each flight fits the requirements you specify in your API request. It is based on weighted parameters, filtering options and connection times. A lower score indicates a route that better matches your needs relative to other alternatives.

Please see:
https://developer.flightstats.com/api-docs/connections/v2