I know. I think that’s because puer is a tea pretty new to international scientists that they are not aware of the need to study it yet.
There are, however, a few studies in China involving the observation of caffeine levels in shu cha. They do find various forms of caffeine in puers, and in a particular study even similar ones as that in roasted coffee beans): SHE Gai-Mei et al, The occurrence of 8-oxocaffeine and pyrimidine alkaloids in Pu-erh ripe tea, Acta Botanica Yunnanica, 2007, 29 (6) 713~6
I think the conclusion in another study is more in agreement with our logical assumptions: that the level of caffeine very gradually lowers as the fermentation progresses, but the end product still contain substantial amount of caffeine (from 3.38% of total dissolvable content to 2.23%): The effects of Asperigillus on Post-fermentative Process of Pu-er Tea, Acta Botanica Yunnanica, 2008, 30(5) 624~8
These reports are only in Chinese 
and I have not found any concerning the content change as the tea matures
and I have not found any concerning the content change as the tea matures 
