Hmmm keep in mind the recording of music began in the 1880s. But they sounded awful. Microphones started to improve in the 20s and 30s. Technology improved because of sound coming to movies. So the songs from the 1900s were available (as sheet music, as piano rolls, and as acoustic recordings that didn't fit with the sound quality we expected in the 60s. WNEW NYC was playing some original recordings from the 30s and 40s in the 1970s. Benny Goodman and Frank Sinatra were core artists and their hits were in the 30s.