Do you think that anyone would have had come into the session with a chart of at least the form for this tune or do you think it just evolved? It seems like it would be a real bear to talk someone down on this tune without a piece of paper to at least serve as a road map.
you know, in all my reading on the great man i have never found any mention of whether he read or wrote charts or manuscript (that i can recall).
i think each member in the band were creative giants. john paul jones is a genius of course, jimi was already a legend from his yardbird days and plant had oodles of blues influence. i think each song was created differently.
i can imagine that for black dog jimi played the riff, bonzo put some drums to it and plant suggested doing the free singing between. jonesy probably arranged the rest of the structure with a lot of arguments with plant.
i can guess that good times bad times was inspired by bonham doing that weird beat and the rest fell into place.
songs like thank-you and the rain song might have been jones started
songs like since i've been loving you and dazed and confused are actually highly original covers of blues standards.