There are "rules"- for keeping order- that are mostly unwritten... the rules are mostly just an agreement to seek an orderly expression of an idea among peers. This works when the people involved are somewhat accomplished on their axe, and have some agreed upon vision of their role within the group.
Mostly jazz is about interpretation, and that means improvisation. So in the 40s and 50s you got a lot of nimble, complicated melodies over the changes to "I Got Rhythm". Be-Bop. That melody was hidden within those chord changes, but you could derive a whole slew of new melodies from those I-VI-II-V chord changes also. And then soloists- even the whole rhythm section- would take it out of the box and run with it. It got absolutely crazy, and some ripping cool music came of it.
Lol, didn't mean to run out of the box...
Jazz is, in many different ways and with many different approaches, about interpretation of a musical idea. I guess.