Most vintage Epiphone Guitars were made between the years 1928, when the company changed theer name to Epiphone, and the early 1970s. It wasn't until 1930s that the company changed their emphasis from banjos to guitars.
Epiphone guitars constructed prior to 1937 are scarce and high quailty. However their less modern neck and smaller body make them less popular, and therefore less valuable. Models built from 1937-1956, when the New York production models of the guitars ended, are more valuable and more sought after by collectors.
CMI, or The Chicago Musical Instrument Company, who owned Gibson, acquired Epiphone in 1957. CMI got all of Epiphones parts stock in the deal and these parts were combined with Gibson parts from 1958 to 1961. Guitars with these combined parts are highly collectible.