Having different iteration constructs or having multiple versions of the same was not untypical on a Lisp Machine, which booted into a single Lisp runtime, but

Having different iteration constructs or having multiple versions of the same was not untypical on a Lisp Machine, which booted into a single Lisp runtime, but which contained several different Lisp dialects and their language constructs. That way one did not need to reboot the computer to use a different LOOP variant - because the Lisp image was shared in the OS. The LOOP code you mentioned came from MIT and Symbolics from the 70s/80s, when multiple Lisp dialects were under use and sometimes, on a Lisp Machine, in the same runtime. The original MIT LOOP implementation had a single source code, which could be loaded into different Lisp dialects and systems. The CL standardization of LOOP was more than ten years later.