There must have been a design change back around the 50's/60's. This illustration of a PC from Stewart Christie's catalogue (same as Sandford's earlier one) has buttons on only one side -

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whereas the one I have made by them in the early 1970's has the buttons both sides. Also their "Montrose" is single-breasted, more like what other places call a "Kenmore" nowadays -


This is the same one although my figure is hardly as svelte as the illustration -