I'd also heard, from Jerry Epstein (who did the transcriptions in the Warner book), that the Warner's only recorded a verse or two on tape, while Anne Warner took down the complete version in shorthand. It had to do with the dearness of recording material: tape (and its predecessors) was expensive (and during the wartime years, scarce) and therefore never in plentiful supply. So recording only a verse or two was a conservation measure.

--Charlie Baum