It's a surprisingly rare one, and I agree with mid to late '50s.
It is not common, so there is some mystery around it. There is a 3/4 size (typically burgundy felt) and this full size version (I've only seen the blue).
Both are equally tough, but not impossible. I remember it taking me about 2 years to track down one of these, but a few have surfaced since then.
That doesn't add much insight here, but hope this helps a bit!
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