If so why? In other words what determines territorial sovereignty? Maps show the Sahara under Moroccan control since at least Medieval Times under the Almohad and Almoravid dynasties (although it is ironically more the other way around as these powerful dynasties originated from the south). I know this isn't a popular subject but I hope someone would at least be able to answer what determines legitimate sovereignty.
A good resource is the non-binding ICJ advisory opinion issued in 1975. http://www.icj-cij.org/docket/files/61/6197.pdf
It essentially holds that there was some contact between certain nomadic Saharawi tribes and Morocco, but not enough to establish sovereignty or have them be considered subjects of the crown. That said, advocates for Morocco either decry the advisory opinion or interpret that limited contact as proof (despite the fact the opinion says otherwise).
Another landmark document in the conflict is the Madrid Accords, when Spain was in a hurry to give up the territory. https://en.m.wikipedia.org/wiki/Madrid_Accords
/u/rkwan (partially) answers your question in this comment to a similar question from 2 years ago.