John F. Rumpf did a type study in his book, Patented Transitional and Metallic Planes in America by Roger Smith and Plane Makers of Wilkes-Barre Pennsylvania. According to him there 13 types between 1892 and 1901. In 1901 he sold his operation to Stanley and they took over the manufacturing.
I haven’t determined if these two (the #5 and #6) are one of the last ones he made on his own, or one of the first ones after Stanley took over. I’m thinking they are after the sale.
EDIT: Some new information.
The best way to tell the difference between a Siegley made and a Stanley made is the cap iron.
If it has a checkered diamond pattern it’s a Stanley version.
Also Siegley never put his name on any of his planes, except for the
number two adjustable which had a small logo with the patent date on it.
Jacob Siegley never made transitional planes, or a bench plane with a lever cap.
The book’s only $15 and well worth it if you will be buying Siegley planes.
-- Master hand plane hoarder. - http://timetestedtools.com