It's certainly possible. The Pinans, in general, are derived from a number of kata, with kusanku being the seemingly primary inspiration. My guess is that he felt that 3-5 aren't beneficial enough to the system as a whole and you can get everything you need from them from kusanku, passai, and chinto.

Soken Sensei only learned Pinan Shodan and Nidan from Nabe Tanmei according to Soken Sensei’s own written records as well as all his interviews. He did demonstrations in the 1950’s with Chibana Sensei and his students and often demonstrated kobudo. He was also good friends with Nakama Chozo. Although he saw and understood Pinan 3-5, he never like Pinan Godan according to his students that I met. He like Pinan Yondan though and its relation to Kusanku. In his Yozadake class in the early 1970’s he did teach his adaptation of Pinan Sandan and Yondan according to a couple of those students but never Godan. Several students of Soken including Kise, Arakaki, Inoue, and others had their own adaptations to Pinan 3-5 that they learned from elsewhere and kept and modified. The more common Pinan 3-5 associated with Matsumura Seito are from Fusei Kise Sensei but are technically Kenshinkan and not Soken’s MS via Nabe. 
 

it was mentioned that someone was close to a Shureikan dojo under Seijun Kina. It should be noted that although he trained with Soken, he was also a Matsubayashi yudansha and he teaches several Matsubayashi kata instead of MS versions.