I must admit, I've been too far removed from the volume licensing to remember how it worked. It was definitely cheaper than retail and I remember 2016 and beyond you paid by 2 physical cores each, at least for datacenter.
All I recall was that they changed the licensing terms twice in ~5 years, and the forced minimum of ~500 users for enterprise put one of my past employers into a bind.
I would not be surprised if they had changed it once or twice since.