Dating a "Federal Electric" breaker FPE

I’m trying to document a date of construction for a building, which has “Federal Electric” breakers.
“Federal Electric” was one of a variety of similar brand names used for what became Stab Lok breakers.

I am aware of https://inspectapedia.com/fpe/FPE_History.php
Which goes over a number of the mergers and splits this product line has taken, but it’s sparse on the early history.

Anyone have a reference to when the Federal Electric name was retired?

If it’s a StabLok panel, they stopped making them in 1980.

I need to narrow the date to between 1950 and 1957. The “Federal Electric” trademark, as far as I can tell, was discontinued before 1960.