"Beiderbecke would have been a far better musician if he could read..."

Maybe, maybe not. One thing we can be a bit more sure of: if he did not use unconventional technique (in violation of the "rules" an "educated" teacher would have enforced), he would never have played some of his most original licks.

Another similar case: Rev. Gary Davis. Like many other unschooled blues artists, he used his left thumb to fret the low E string on the guitar, which is absolutely verboten in the classical/conventional context ~ and which is the only possible way to play certain phrases.

Also consider the many great blind blues originators; they certainly assimilated a lot of theory, in some form or another, but undoubtedly did not read sheet music.

The ability to transcribe music in standard notation may once have been the only way to "record" music for posterity ~ but (in case you haven't noticed) we now have the ability to actually record sound, and have had that resource available since at least a half-century or more before any of us were born.

A recording doesn't show you how to play a piece as well as sheet music (nor as well as tablature, which is actually better than standard notation for showing how a piece is played on instruments like the guitar), but it certainly conveys how the piece sounds ~ exactly how it sounds ~ far better than does any written or printed transcription.