Using more then 2 Custom UVChannels on Landscape

I’m trying to move the texture coordinates calculation to the Custom UV Nodes. In the documentation I couldn’t find a limit of UV channels. Therefore I assume that 8 are possible, because they are displayed in the material attribute Node (MakeMaterialAttribute). I am currently using 7 of them.

But only UV0 and UV1 work. A look into the shader code shows:
#define NUM_TEX_COORD_INTERPOLATORS 2
After configuration of the material there should be a 7?

Is the value “Num Custom UV’s” even considered in the shader code? Or is there a limit of 2?