That is too funny! Great pictures on the link to your other page.
Here are my thoughts. This is definitely older than 1960s that you mentioned in the Victorian Sweatshop. .Is yours a treadle and hand-crank operated? Is it a Coffin top or just sitting on a desk of similar color to the top?. How big is the throat area? How light (weight) is this beautiful Enterprise of Nicholl's? Purchased new in 1920s seems rational but a bit earlier wouldn't surprise me either. What is amazing is that you have the manual and this one looks brand new! What a treasure! You should take a field trip to England to find more of them!