I just want to make it clear that if you are a huge of of AMD, then you can run MAX of 13 GPUs on a single motherboard as shown on this video:
https://www.youtube.com/watch?v=miUoqnUqk9M&feature=youtu.be&t=3285

However, if you are a huge fan on Nvidia then you won the lottery, you can indeed run 19 GPUs on a single motherboard all from the same vendor

The interesting question here is,
When will AMD remove this limit of 13 GPUs, and why their drivers search for P106 after you have reached the 13 GPU limit and will not accept any further AMD GPUs?

Does anyone know?
I think BBT mentioned that he has opened a ticket for AMD and i doubt that he has already gotten an answer on that