because the description was deemed unsupportive to the invention. The patent also had other problems as it was badly drafted according to Chinese Patent standard. As a matter of fact, it was invalidated in UK and other countries where it is more strict to grant exclusive right for inventions. Most US patents, especially those written in the early 90s, are not intended for China and would be unlikely to survive "supporting" challenge in China. GSK has given up one of their CN patent for the same reason. There are likely to be more US patents like those to be identified. It takes good patent agents to pick them up, fight, and win.
The purpose of paragraph IV is to establish the generic drug would not infringe. Normally US is where patents are most difficult to be designed around. If that part can be done in the US, it can also be done in China.
