F visa renewal in Yunnan with an invitation letter from Shanghai

My husband and I are researchers on an F working with a branch of the CDC and we have an invitation letter from them. Our research is in Yunnan. We got a 30-day F in Bangkok (last day is August 29th) and now are having trouble renewing it because we live in Yunnan and the invitation letter is from Shanghai. (Previously, this was not a problem.) I have heard that getting it renewed anywhere in China is now a problem if we were not in the US when the F was issued. The PSB in Dali seems to think we can get the extension in Shanghai. The director of the government department at the CDC in Shanghai said that they were not sure if we can get it without going back to the States. What is the truth?