Actually, the 100-day cough does exist. I didn't believe it until I caught it about 5 yrs ago, and since then I've had 2 to 3 bouts of it which lasts for about 3 mths each time. It's a dry incessant cough that makes it tough to even talk, e.g b4 I could finish a sentence, I would have to bend over to cough, so you can imagine how miserable it was to maintain daily life. No amount of expectorants, cough syrup, Woods, Pi Pa Gao, etc. and what-have-yous can cure it. Perhaps the only upside is the incessant coughing helps to develop the stomach muscles(?).
Finally, the cure for me was to take "tong chong cao", i.e. the Chinese medicine "winter-worm grass/herb". This is a worm in summer, and during winter it kind of goes into hibernation and subsequently, with the action of some micro-organism, the worm turns into a root kind of herb, hence become a "cao" (grass). I read this in Zaobao recently.