Oscar,
I found a small handful of these chips in Kingman, Az. at the swap meet. It was a few years ago, and I did some research at the time.
On the Over50Vegas.com site, I found reference to W.D. Shoulders as part of the casino personnel of the El Cortez. It can be found in
a Christmas 1955 issue of a Jack Cortez "Fabulous Las Vegas" magazine, page 138. I could find nothing that associated him with Yerington.
I was told, second hand, that some of the NS chips were found with some chips from Yerington.
That's the sum of the information I have. Hope it may be of some help.
Keep doin' what your doin' !!!
Doug