Mine has a supplement from the 1960's, I think. I'll have to look in it and see what the numbers are.
In the very back there are note pages. In most books these are blank, but in this they are ruled with music staffs. I can just see a choir copying down some music that a choir director had written up on a chalk board. There was no such thing as copy machines in 1940.
I believe the mimeograph already existed...