Thank you for the link and I need to spend some time to read the details. It was stated in the paper I read that tracking one of the proving flights failed but other flights had data which correlated to part of an aircraft's flight path.

I agree with your analysis that some pre-knowledge of the track is apparent here and therefore more fully blinded independent experiments would be needed to add credibility.

Given the number of airline flights at any one time and the near constant WSPR radio traffic I would have thought there is enough raw data out there to conduct further research. There may a PhD in this for someone :-)

I do worry, as implied in your emphasis, that the temporal resolution is very low. Given that the transmit time of all symbols is approx 110.6 seconds [1] plus the time for a WSPRnet station to decode a message will translate into spatial errors of various magnitudes proportional to the speed of the target aircraft, but perhaps this has been factored in.

I do remain intrigued enough to try and learn more about the robustness of the techniques.

[1] https://swharden.com/software/FSKview/wspr/