Simmons Hardware was in business from 1872 to 1940. Shapleigh Hardware was in business from 1843 to 1960.
1922 to 1930 Simmons Hardware was owned by The Winchester Company. After WW1 Winchester went into the production of a full line of hardware items in an attempt to utilize their foundries/facilities previously used for production of war related products. Winchester found while their production ability was great, they were unabe to distribute their products. Winchester bought Simmons to use their established distribution facilities. In 1930 The Winchester-Simmons Company went into receivership. Winchester's hardware plan was determined a failure. Winchester and Simmons split back into 2 seperate companies.
Winchester returned to firearms production. Simmons struggled through the 1930's. June 28, 1940 Simmons and Shapleigh announced Shapleigh had purchased Simmons Hardware Co.
Shapleigh Hardware continued production of their flagship brand "Diamond Edge" and began production of "Keen Kutter" items as well.
I have seen this buttplate on another KK gun before. It may just be one of those mystries.