In my bayo collection, I have a 1917 dated SA to match my m1903 1917 dated rifle. I also have the older "two-tone" and newer
parkerized (1918) bayos. So far, I have only been able to find info saying the 1917 ONLY had a complete blue job. In fact, my 1917
unit is beautifully blue. Prior to 1917, the bayos were two toned and from 1918 on parkered. Most pictures of WWI show the bright
blades on the m1905 bayo being used by AEF. I have read that the parkering and bluing was done only to subdue the surface
brightness and not for metal protection.