My guess is that planes reach their cruise heading, altitude and speed by the time they get out of range of ADS-B receivers. Since they follow predefined air corridors, location can be easily inferred from last known information. Obviously it won't be accurate if the plane has changed course to avoid bad weather (see: https://en.wikipedia.org/wiki/Air_France_Flight_447).

Filed flightplans and dead reckonging are sometimes intermixed when ADS-B coverage is poor.