Though this wasn’t always the case. A white label didn’t have to be a promo. For some countries like Argentina, it could have a standard lp face with words translating to “Not for sale. Promotional copy only” or something on the lines like that.
Standard Lp face (Promo) for Empire Strikes Back (Argentina): The words “Difussion prohibida su venta” are the words stating that it is a promo copy.
But it can also come down to the distributor. For Star Wars, there was a promo but it wasn’t a white label either.
Standard Lp face (Promo) for Star Wars (USA): The words “Not for sale” mean it is a promotional copy.
RSO were generally known for making white label promo’s for the Star Wars soundtracks but in 1977, the rights for the Star Wars soundtracks were given to 20th Century Fox (As they were the a part of the production set for the movie) but weren’t particularly known for white labels (giving reason why there wasn’t one). Until 1980, when the rights were given to RSO. They made the Empire Strikes Back and Return of the Jedi soundtracks. But, according to https://www.discogs.com/John-Williams-Star-Wars-Return-Of-The-Jedi-The-Original-Motion-Picture-Soundtrack/master/55429, there is no documentation of a white label promo for Return of the Jedi. But some speculate that there is but you can never really be sure. Because the images provided (if provided) are from those who own the album because you can edit the database. I am a collector and I’ve trying to find these for years. Given why I have so much knowledge on this topic.