Nakaya mentions the Channan forms and Kusanku (Kwanku in Shotokan) forms as the basis for the Pinans. But, it is also mentioned the Itosu was attempting to simplify the forms as the Naifanchi were too difficult for the school children. I must confess to seeing a bit of Naifanchi (Tekki), Passai (Bassai) and Chinto(Gankaku) in the Pinans.
Of course, there are several versions of these kata being practiced today. What the kata looked like when Itosu put together the Pinans is anyone's guess.
For Uechi-ka, the Pinans offer a valuable reference. The influence of the Pinans is quite evident in Kanshiwa (just as the evidence of the influence of Gojushiho in the application of several Uechi kata is evident). For Uechi students then, studying the Pinans, and there theory of defense can be quite helpful. It seems to me the pattern of the kata demonstrates an understanding of group psychology and the tactics of dissipating and isolating members of a group remains a viable strategy today.
For Uechi students, who seem in constant search of the "Lost Kata", the story of Itosu and the Pinans may also offer encouragement. We are not the only style to lose kata. And, just maybe, the folks who passed the kata on to us saw little need to preserve a particular kata, perhaps believing that the rest of the training they shared with us provides us with all the insight and tools necessary to our continued training.
Robb in Sacramento