I don't know if you made your point badly or not, but your tone surpised/confused me. You begin by saying, "But he doesn't track down the source of the quote, only of a famous usage of it by JWZ." Later you add that Friedl as the author of such and such "is only interested..." in so and so (my emphasis). In both cases, I read that as criticism - as if Friedl failed to do the important thing that you were now doing. In this post again you you say that Friedl is "not really interested" in the source.

But, in fact, Friedl did track down the source of the original quotation - to a reasonable degree of certainty. It's the same source you found. So I guess I don't see what Friedl didn't track down.