A couple of points about catalogues and pricing in the old days. The first comprehensive Charlton catalogue devoted exclusively to paper money was published in 1980 (I exclude the ca. 1955 edition because it only listed government notes, and no Bank of Canada after 1935). In it we find the 1937 Osborne $50 at $1,400 in UNC. That catalogue was eventually expanded into the three we have today, Government, Chartered and Merchant.
Secondly, I do not agree that the prices in early catalogues (1960s) were just made up. I can tell you three anecdotes which will explain. A friend of mine bought a gem Unc 1937 Osborne $50 from a dealer, I think about 1969, and the $75 price sounds about right. He had a talent for picking quality notes, and it is one of the few surviving gem uncs in the hobby - most are pressed EF or AU notes, regardless of what the slab may say. Anyway, if I recall the rest of the story correctly, his acquisition was belittled by more experienced collectors who assured him he overpaid.
Another story, which I believe to be true, concerns Jim Charlton who had picked up a couple of 1935 English $500s about 1960. He tried without success to sell them for $525 each, and ended up depositing them at his bank. One needs to understand that $500 was a lot of money back then and way out of reach for most collectors (especially this one - I was making a whopping 35¢ an hour - before there were any minimum wage laws.)
Finally a story about a 1935 English $100. I know it's true because it happened to me. In those days I was more interested in chartered bank notes (still am). I'd picked up the note for a little over face, and since hobby dollars were hard to come by while paying down a mountain of student loan debt and a mortgage, I consigned it to an auction. It sold for a whopping $110, and after the commission was deducted, I was left with exactly the face value. I'd have had my money quicker had I simply deposited the note.
Anyway, that's how it was - from one who was there.