I think this is an interesting (although, possibly OT) discussion in itself.
I mention it because jazz, like much photography, is a pursuit that depends on a combined knowledge of technical theory and a modernist aesthetic.
When someone talked about "theory", I must admit that I connect that term with knowledge that have been accumulated in academic institutions. I.e. explanations for observations that have (hopefully) been published in some publication, scrutinized by fellow academics, generally accepted after some time, and eventually incorporated into some kind of canon for the field. Though I must admit that I know less about the process in human sciences than natural science.
In the humanities, theory is manifest in works themselves, and often not in journals. HCB did write some in Images a la Sauvette about The Decisive Moment. But talk of what he was doing was common amongst those connected at that level of the enterprise, both in and out of Magnum. This kind of knowledge is traditionally passed along in the oral history tradition.
When you seem to propose that skill learned through listening to great masters (on your own) or at jam-sessions or through informal meetings with fellow artists is also "theory", I think that is a confusing choice of terms.
It'd be more accurate to say that the "community" is an active learning community, and that "theory" is indeed what gets passed along as verbal history in working collaborations and to a degree in more informal encounters. And in fact, the best theory gets distilled and disseminated this way, and in a way that peer-reviewed journals in educational institutions will never equal.
Thelonious Monk did go to Juilliard, but his most important innovations were his alone. He did write them as musical works in musical notation. You can read that as the primary literature, as well as his improvised performances. To understand and explain these innovations in harmony and melody though, you really had to be talking either to him, or to people who worked directly with him, or to people who spent a lifetime studying him.
There are a dozen or so explanations for the technique of adding the sharp-5/flat-6 to the major scale in modern jazz (known sometimes as the "bebop scale"). You will only get one or two of those explanations from any professor of music. To get the deeper explanations, you have to seek out and learn directly from the people who spent a lifetime learning how to exploit this beautiful bit of theory. [Barry Harris, a jazz legend, teaches us to use the flat-6 diminished scale as a kind of rosetta stone that allows one to pivot easily between keys that otherwise seem only distantly related to traditional theorists. It's not a simple lesson, but takes years to master.]
But these are not merely informal encounters. When one spends months working in the band of a top musician, one gets the opportunity to learn -- by trial -- all the things that go into the making of that musical style. Very few of these things are taught in the conservatory...or at the jam session either for that matter.
I can agree that the mathematical structure behind choice of harmony, rhythm and melodic lines may well be similar as taught at a conservatory or at a jam-session, as it may be a matter of condensing (potentially) centuries and millions of culturally (or evolutionary) "preferred" patterns. I have 88 notes on my piano. For "musical theory" to be of any practical value to me playing, it has to say something about what notes to choose, when, how hard to strike them, in different contexts.
Some of this knowledge flows in and out of the academy. Dr Roland Wiggins was a Juilliard theorist trained in esoteric theory in 20th c. music. Many jazz musicians in the 60s and 70s sought out Wiggins to teach them some of the things he had learned and knowledge he himself had derived. Some of this learning took place subsequently in the university (e.g., Yusef Lateef did a doctorate with Wiggins, though Lateef himself was equally a source in their dialogs), and some did not (e.g., Coltrane sought out Wiggins privately to teach him about synthetic structures, which he later incorporated into his later works).
