How to map non-US routes?

From what I understand, calling DecodeFlightRoute on any non-US flight will fail with “unable to decode”

Yet, on your live flights page you’re able to draw a route on the map for non-US flights. Can you share some insight into how you (and we) can do this? Is it based on data not available from the API or are you somehow extrapolating it?

Thanks for your help.