There are also many unlisted varieties existing, for example this stampless cover from FU CHIN (Kerr 41) in blue instead of purple.
I have a list of all the ones that have been reported somewhere or seen by me. In Chiu's Supplement he gives a list of them mostly from Rehe and places close to it.
I have scans of about 20-25 unlisted ones from Dongbei that Chiu does not list.
I wrote an article once about the ones from the "East Mongolia Autonomous Government." It is in The China Clipper.
So far from the Dongei, there are stampless covers from many of the places retaken from the bandit armies by People's Militias.
Hugh Lawrence showed an amazing collection of them from East China (Jiangsu and Anhui primarily). I will ask him if they exist from other places in the LA, outside of the Dongbei.
Altogether I have seen about 50 different, and about 25 from Dongbei.
I have bid on them but have had virtually no luck at all. A list will be given, and B&W scans of what I have seen in my book.
There was no color scanning when I held them in my hands.
Mr. He Hong once wrote about their existence. (None listed by him then.)
There was an article in Mr. Poon's magazine Stamp World fairly recently. Has anyone seen it?
That is the best I can tell you at the moment. I pray it helps you.