Mathew, like so....just reverse the process he used.
;; I would still use "date" in lieu of "cdate" since you can easily
;; add/subtract days from it without worrying about spanning months & years
(setq cdate (+ 113877 (read (vl-list->string (reverse (vl-string->list (rtos (getvar "date") 2 0)))))))
(vl-registry-write "HKEY_CURRENT_USER\\Software\\WinSpec00" "Data" cdate)
(setq regdate (vl-registry-read "HKEY_CURRENT_USER\\Software\\WinSpec00" "Data"))
(setq regdate (read (vl-list->string (reverse (vl-string->list (rtos (- regdate 113877) 2 0))))))