So I’ve read that the Jacob Siegley got his first plane patent in 1878. Most of m information comes from 2 sources. Patented Transitional and Metallic Planes in America by Roger Smith and Plane Makers of Wilkes-Barre Pennsylvania by John F. Rumpf.
Siegley made his planes until 1901, when Stanley bought him out and continued making his planes. In 1903 he signed an extension to allow his name to be used in additional planes (not sure what that really means) but he also was paid by Stanley for future consulting.
I believe this plane must have been manufactured b Stanley after the 1903 date. I’m not sure much after that.
-- Master hand plane hoarder. - http://timetestedtools.com