The "ninth chord" that Rameau, Kirnberger, Marpurg or Koch (inter alia) discuss during the 18th century is the chord formed by a triad and an added ninth, and its explanation is always through a "chord of supposition", i.e., the supposed root is a third above the lowest note of the chord, since chords that spanned more than an octave were not "acceptable"
70-80 years laters, in harmony treatises like Reber or Richter (around 1850) the dominant ninth chord has earned its status as dissonant chord along with the seventh, and it is considered as a dominant 7 plus a third, its root being the root of the dominant seventh. Furthermore, diminished and half diminished seventh chords are now considered as a dominant ninth without its fundamental.
My question is: who was the first theoretician that considered this chord as an acceptable entity, and placed it side by side with the triad and the seventh chords? Who started thinking about chords as a stack of thirds that could exceed the octave? Who was the first to propose that diminished and halfdim chords are rootless dominant ninths?
Any help would be much appreciated.