Are Step Chucks Serialized For 10EE Lathes?

I had a 10EE quite a few years ago that I sold off. It needed work and I just don't have the space to spread things out to work on it. I kept all the tooling for it in the hope at some point in the future I might move into a much bigger shop space. Which I expect will happen in the next few years. And then might take on that sort of project. Anyway, I know a little bit about 10EE's.

I bought a "box lot" of step chucks for what I thought were all South Bend Step chucks, for my Heavy-10 South Bend lathe. In going through them, I found this one step chuck slightly different than the SB step chucks.

Is it serialized to a 10EE? S/N seems to need one more numerical digit to be for a 10EE. Step chuck is 6.5 inch on max OD.

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10EE's didn't go into production until late 1930's, so 4 digit 2061 S/N doesn't seem to fit EE. needs an addtl digit.

Serials from S/N Reference book....

I believe that is just an EE part number- Monarch's p/n for the step chuck.

I have a couple of Monarch step chuck closers. One or more of them seem to be off size as compared to what Hardinge sells for step chucks.

I just wondered if it was serialized. It's practically the same as the similar SB ones I have. So just going to keep it w/ my SB stuff.

My step chuck body has no markings but my drive plate carries the serial EE 2597