Palgwae forms were developed in the midpoint of the KTA (second coming) to further unify taekwondo. The represented kwans within the KTA, which I figure were more than 9 at that point but 9 being the major players, developed the palgwae poomse, almost from scratch. I say almost because the schools influence was heavy on the development. For example (fictional btw just and example that could happen) the chung do kwan school developed the 4th form and they decided they wanted to include the diamond block backstance technique because it was prominent in their own schools series of forms. Thus schools added their own flavor to the forms, which actually went away from the purpose of getting away from the kwan system and unifieing taekwondo.
You can actually see the older influence on the palgwae forms as they are all very similar to karate. Much lower stances. There isn't one hi stance in the entire palgwae series to my knowledge.
Later on after the KKW was spawned from the KTA, the Taeguek poomse were developed. Once again the kwans helped develop in association with the KKW, but this time it was totally from scratch.
Anyone else have other info?
BTW whitebelt, I'll go back and see if I can get some dates for you, this is just off the top of my head.