I'll try to help put a date to it.
For starters, here's mine, which is easy to date, as it has the broad arrow and date found on kit bought under government contract for the military:
You'll see that the typeface used is not the same as on Duke's. It has closed loops on the g and a, in common with most faces used in books (except in italics). His has open loops on those letters, similar to many people's handwriting.
Moore and Wright Catalogues in the ITCL don't use the open loop face.
I do have a later catalogue, this one:
M&W were absorbed into the Neill group in 1970. The catalogue is undated but refers to events in 1978. Here's the internal illustration of the available workshop squares:
Different lettering again, all in capitals, with the model number and standard.
However, the cover of the Neill Group catalogue does show the M&W logo using the new style lettering, even though I can't spot it shown on any of the products.
So on that basis, I'd guess that Duke's square was made in the 1980s or later, which I still think of as "quite recent".
But it's still going to be a good one!