WRA Headstamp for .35 Winchester?

According to Giles and Schuey the last box for the .35 Winchester was the 1939 box with the Western Cartridge Company call-out. The drawing of the cartridge on the front of this box has a W.R.A. CO. with W.C.F. headstamp. I have seen several of these boxes and they all had the W.R.A. CO. headstamp cartridges in them. Now I have a box that has five WRA headstamp cartridges with .35 WIN below the WRA. Does anyone know when Winchester started using the WRA headstam for this cartridge? Thanks. DRJ