Most of people who sent the application in 2001 have been landed in Canada. Only quit a few people have received the 2nd letter since they submitted application after 911 in 2001, but still waiting for Backgeound check.
Here is my question to you:
1. When you cam to USA?
2. How long you have worked in China?
The questions are the key facts which may effect the processing time.
Good luck to you!