From what I can tell those two groups never overlapped in any parts books.
Maybe once Chevrolet retires a group number it's gone and they don't waste time researching to see if a new part might fit in an abandoned group...just take the next number and run with it.
Also, they changed the wording from "Thrower" to "Slinger", so that might be another reason to give it a new group.
Mike B
