So here is a fun one. If you look into http://www.facetdiagrams.org, and you narrow your search by year, I think you will see that the oldest design found, is a design listed from 1944. It is 01.229, Goldstein Round. The design itself states that it was from “Goldstein, Edward; Off P Gazette, 1 Feb 44, p160” The Off P Gazette is short for Official Gazette for Patents, and if you follow the link provided and go to page 160, you will see this design.
So if this counts for 01, Feb 1944, that would be the oldest yet. It is actually fun to search for older faceting designs on this Off P Gazette website. I’ll bet there were some very interesting historical events surrounding early facet designs, and their patents. I’ll count this design because I know of several older designs, and I still challenge USFG members to search for older designs.