Ulbe, I tend to believe that (a) it's not the same color, and (b) that the number could have been the result of a typo or transcribing error.
In my list, I have "Grigio Finanza" listed as AR-728 (for 1987 only), AR-744 (for 1970 only), AR-746 (for 1977-78) and AR-758 (for 1982-88).
"Grigio Antracite" is listed as AR-746 (for 1971-79), with a note that there are some documents that refer to this color code as "Grigio Finanza" (for 1977-78).
Based on other colors I know of, it is possible that the numeric color code has been reused for different color names over time, but that typically did not happen within the same decade.
Furthermore, I never figured out what the difference between ARS and AR designations is on the Glasurit color cards (I presume different paint systems), as this is not an Alfa Romeo designation and only used by Glasurit.