The evidence is in numerous books. My experience working with assembler dates back to the early 80's with 6502 and Z80.
You only have a limited number of registers, when you run out of registers, this doesn't mean you can't call any functions, it simply switches to the stack. Go read some books or search online.
Like-wise, if you nest to many function calls you will run out of stack space and encounter a stack overflow.
If too many, those that don't fit are passed on the stack.
This might be useful: Calling convention - Wikipedia