I’m sure the Sargent #411 was introduced to compete with the Stanley #5 1/4. The Stanley #5 1/4 came out in 1922, so subsequently the Sargent #411 and #411C was introduced in 1926. The #411 was produced until 1947 and the #411C stopped in 1943.
HMike posted a #411C here, http://lumberjocks.com/replies/851679
I classified mine as a type 5. About the only variation off of a type 5 is the cutter adjusting knob is steel on this one (which I just figured out this morning during clean up).
Its Also got a cutter that doesn’t fall into any of Heckel’s type studies.
So far the #411 is the only size I’ve seen with the plane size in front of the knob. If this changes, I’ll post it here. If you have one, let me know.
Here is a later model (1947-ish)
Cap is solid on back (1940s at least)
Cap looks to be Zinc plated (well worn, except back of cap)
Adjuster is two-piece
Adjuster screw is steel, NOT brass coated
Over all this plane looks like one of the last 411s produced and should contrast well with your older 411