The regulation equipment for a fully-equipped British archer at the battle of Agincourt (1415) was: “1 longbow of yew; 3 strings therefor; 1 quiver (leather) with strap; 9 clothyard arrows, goose feathered, steel tipt”. Breeches were optional: to be worn if one had them. (see Dorrington Ms. 1416/233g, P.M. 244b, Brit. Mus.). In a busy set-to like Agincourt, an archer would be expected to shoot off “ye whole nine yardes” within the first 1 or 2 minutes or so of battle. If there were any Frenchmen left standing after this, he could collect another standard quiverful from the armourer’s mate, and polish them off.
This statement is about as well attested as any from WW2. Better, if anything - for we know, without needing any laborious, hopelessly contrived calculations, that 9 arrows were precisely “9 yards”.