What do you mean by this? Do you mean people who tend to like multipe groups from the same company or people who are dedicated to the company as a artist brand?
I would say SM is the only Big 3 that I have seen that have true company stans. Certain people tend to like multiple of their groups and are dedicated to the company as a artist brand.
For JYP (at least for me) I haven't seen that many truly JYP stans. IDK, maybe because they had a dry spell and most people just seem to be Onces, iGot7/AhGaeSe, former Wonderfuls etc I haven't encountered that many JYP stans in either fashion.
As for YG I don't know what people mean. From what I see widespread commitment to YG as a artist brand died with 2NE1. You have lots of people like me that stan or like many of their acts but we don't claim YGE, though many outsiders label us that. Also I see people that are just big fans of one group be called "YG stans". I think there are only really YG stans in terms of stanning a lot of their groups but not like what SM has at all.