((41.#1=(2.#2=(3))) (14.#1#) (12.#2#) (12.#2#) (12.34)) in xyzzy does not appear in the normal list.

#1=#1# indicates that Common Lisp is referring to the same data.
xyzzy is about 60% compliant with Common Lisp, but with Common Lisp, you can disable the display of shared structures by setting *print-circle* to nil.

 (setq*print-circle*nil)

(ins4nil'(123))
→ ((4 1 2 3) (1 4 2 3) (1 2 4 3) (1 2 3 4))

However, after trying the above with xyzy, it seems that this setting does not take effect (bug?)

In this case, the contents of the data output by ins remain the same, since it only clearly states that they share the same cell data.

((41.#1=(2.#2=(3))))(14.#1#)(124.#2#)(1234))
       '((4 1 2 3) (1 4 2 3) (1 2 4 3) (1 2 3 4)))
→ t

If you change your mind and decide not to share the structure (you create new ones every time instead of reusing them), naturally the shared structure will no longer be displayed.

 (defunins(xfs)
  (cons
   (append(copy-tree f)(cons x(copy-tree)))
   (if(nulls)
       nil
       (ins x
            (reverse(cons(cars)(reverse f)))
            (cdrs)))

(ins4'(a)(b)(c))'(123(4))))
→ ((a)(b)(c) 4 1 2 3 (4))
   ((a) (b) (c) 1 4 2 3 (4))
   ((a) (b) (c) 1 2 4 3 (4))
   ((a) (b) (c) 1 2 3 4 (4)))
   ((a) (b) (c) 1 2 3 (4) 4)

In the above section, copy-tree deep copies the list f and s.