I think I can tell you a bit about pollen flying here from Morocco. We used to have tons of it but I have never seen a plant making seeds if there are no males near. Also Moroccan Kif (now called Beldia) landrace was harvested in August, so if you were growing tropical sativas (NLD) in Southern Spain they have not even sexed. But I began growing birdseeds when I had no NLD seeds and I have never seen them pollinated. Anyway they have replaced the strains and the growing methods so I guess they cull males there. Anyway it seems the pollen that arrives here is not viable.
https://www.researchgate.net/public..._from_North_Africa_to_the_Southwest_of_Europe
www.biblioteca.uma.es/bbldoc/articulos/16719712.pdf This link seems it doesn't work, just delete the http://
https://pubmed.ncbi.nlm.nih.gov/23208276/
https://www.uco.es/rea/publicaciones/andalucia/malaga/Nadia_variations_2013.pdf
What about ditch weed in the Midwest?
https://www.researchgate.net/public..._from_North_Africa_to_the_Southwest_of_Europe
www.biblioteca.uma.es/bbldoc/articulos/16719712.pdf This link seems it doesn't work, just delete the http://
https://pubmed.ncbi.nlm.nih.gov/23208276/
https://www.uco.es/rea/publicaciones/andalucia/malaga/Nadia_variations_2013.pdf
What about ditch weed in the Midwest?