I resorted to cons counting to confirm it for my own simple mind and... you're correct! ^_^
; bucket (5 conses) ((a . (b . nil)) . (1 . (2 . nil)) ) ; "frugal" alist (4 conses) ((a . b) . ((b . 2) . nil))
Sorry I don't have time to respond to the rest of your comment right now.