I'm not quite sure what you mean - the Burroughs machines have full sets of display registers (hardware managed pointers to each of the stack frames that were currently in scope - Algol/etc had more complex scoping that modern C-style languages) - a stack pointer contained a lexical level (an index into the display registers) and an offset into that stack frame - there's a variant that's 'stuffed' (essentially a reference to a variable in a stack frame that's out of scope - based on the base of stack)
I think it's important to understand that it's not a C machine, doesn't have a linear address space in the normal sense
you create an in-scope reference within the function - and then 'stuff' it which converts it into an offset from the base of the stack - converts an "indirect reference word" into a "stuffed indirect reference word"
it's what you use to pass by reference ..... but algol supports pass-by-name semantics (of which pass by reference is an optimisable subset) - to do fill pass by name (for a simple example a[i] where i is a global) the compiler will create a thunk (a tiny subroutine, in scope of the place where the parameter was passed) and pass a pointer to it - the tag of '7' means a PCW - when it gets dereferenced as a pointer the hardware does a subroutine call to the thunk in the correct scope
I think it's important to understand that it's not a C machine, doesn't have a linear address space in the normal sense
This is worth reading to understand more:
https://people.eecs.berkeley.edu/~kubitron/courses/cs252-F00...