I'm reading George Russell's Lydian Chromatic Concept right now, and I'm trying to better understand its place (and his) in the history of jazz theory. Was he the first to posit this improvisational approach, or did he learn the basic system from elsewhere?
Todd's comment that it can be "hard to firmly determine what kind of theory was in the minds of early jazz musicians" is absolutely correct.
Nevertheless, I have tracked down a source (The Cambridge Companion to Jazz by Mervyn Cooke and David Horn) that offers the best explanation so far.
It's clear that Russell's book was the first published text explicitly on jazz theory. However, one story claims that Miles Davis was "indirectly responsible for the Lydian Chromatic concept," suggesting that the idea of a chord-scale approach was indeed already present in the minds of at least one musician.
Ultimately my question was an attempt to understand the importance of Russell's book. If I can be frank, my reading of it hasn't left too positive an impression on me. It's not as systematic as I would like a music theory to be, which leads to a lot of circular reasoning on the part of the author. (It also gets downright pseudoscientific at times, but it's hardly the only theory treatise that does that.) But understanding Russell's work as the pioneering work on jazz theory helps me understand its appreciation more. He was very much a founder, but other authors down the line were able to package similar ideas in much more pedagogically minded ways (e.g., Mark Levine in his The Jazz Theory Book).