Semi-Custom means that specific customer orders specific product, and that product is ONLY for the one who orders it.But I am not so sure about this. It may be semi-semi-custom and being used by a few customers... I mean the grab from radeon software is a dll. And there is at least one other obvious customer named Microsoft who literally requested a Zen 2 + Navi APU years ago (Oberon iirc) and has a semi-custom AMD APU in a laptop right now.
Knowing a bit about how AMD works... I feel like what happened here is they are developing a "custom" part for Apple/MS that will then get announced as a new product available to other vendors around the same time a MBP 15 or Surface that already uses it is announced
Xbox and PS4's APUs were different and Xbox's APU appeared only in Xbox consoles, PS4's APU was different than Xbox's and it appeared only in PS4.
That chinese console/pc with Semi-Custom APU appeared only in that console/pc.
That GPU that was ordered by Intel for their 8809 Core i7's appeared ONLY in those System on Packages.
If Van Gogh appears in Apple kexts, it means that Apple ordered it.
And that it will appear ONLY in Apple computers.