I'm not sure whether or not that is a replacement cord but it may be. I will say, I have two 505s and they both have type of cord - exactly.
However, I have a 2C which came with a black cord with the old fashioned round "screw-terminal" type of plug on both ends. It has a metal 'loop' to hang the cord but it's different than the later versions. The metal loop is attached to a collar about 1/2" long that slides along the cord -- e.g., not a molded "loop holder" like the later cords.
And I have instruction booklets for the 2C, 3C and 4C, and they all show the same type of cord that came with my 2C.
Of course we know how notorious Kirby was for recycling photos for subsequent models' manuals, which is really frustrating as it makes it impossible to nail down model specifics such as this.
So, while the "screw-terminal" plug may have been used for the 2C, it could have been changed anywhere from the 3C to the 505.
I believe the first model with a Kirby logo on the plug was the 509.