The Warner brothers concert in New York will not just be them singing (although that ain't half bad), they will also be playing recordings of the source singers, showing pictures, playing recordings of conversations with Frank and Anne, etc. Should be quite an amazing show. They are also doing it in DC next night (3/17).
Back in 1940 it I think virtually impossible to get enough of the lacquer discs to record whole songs. They first had tape in 1950 and then recorded not only whole songs, but also extensive talk with the source singers. It is a matter of immense good fortune that they were able to get recording equipment at all in 1940, as they had no money and no outside support. Fortunately someone (at Philco if I remember) became interested in what they had been finding since 1938, which Frank was able to communicate with his amazing singing.
It is also worth noting the immense improvement in the quality of the recordings that modern technology has made possible for the CD. COmpared to what I had to work with to do the transcriptions for the book, it just blows my mind.