(1) No. Winchester did not supply RIA with nickel steel in 1918.
(2) RIA was able to switch over to nickel steel quickly because their steel inventory was very low. Nickel steel had the advantage of being somewhat insensitive to heat treating temperature whereas carbon steel was extremely sensitive to heat treating temperature.
(3) I'm not sure I understand your third question.
(4) The information you inquire about was published in the U.S. Martial Arms Collector magazine about 10 years ago. I was co-author.
Hope this helps.
J.B.