Ted, the differing character of these improvisations evidences a larger stucture and it is what attracted my attention.
My technical background in music isn't sufficient to offer any more suggestions in that sphere. But perhaps an analogy with chemical physics will provide some insight.
Jazz and improvisation came into formal prominence about the same time as quantum mechanics (QM) became similarly accepted. The intellectual connection being that both incorporate non-deterministic elements not found in classical forerunners. For example, in a quantum system, it's no more possible to know exactly the future configuration of a system than it is to know which chord follows another in an improvisation; in contrast, classical physics more or less assumes the position and energy of particles can always be determined accurately and, as you mentioned, classical composition can be quite rigid. This element of chance in both music and physics was formally recognized, on the one hand, to pick one event, Gershwin publishing "Rhapsody in Blue" in 1924 and, on the other hand, Planck's Nobel prize for using quanta in 1918 and Dirac's prize for formalizing QM being awarded in 1933.
What has happened more recently in electron density work is that new kinds of objective structures have been discovered, largely by Bader. These new structures, called atomic interaction lines, recover some (but only some) of the classical ideas of chemical bonding from the mathematical machinery of QM. These lines were unknown before, but can be directly determined experimentally or rigorously computed from theory. Although many important questions remain unanswered, this head-to-head comparison of theory and experiment verified both and has been performed in laboratories all over the world in ca. the last two decades.
The point I'm leading to is that although contemporary and accurate physical theories incorporate chance, this has not resulted in either the total loss of measurable, objective structure in electron distributions or the abandonment of all classical notions. It just required a highly mathematical definition of a new kind of structure and ways to determine it. These structures were in the electron distributions all along, but they couldn't be extracted cleanly without a new, rigorous mathematical procedure.
Whether this has any significance regarding larger structures in improvisations, I'll leave it to you to answer - musically, in part, I hope.
Regards,
Jim