Tourist L Visa with extention, cancells origional L type?

I have (had?) A tourist L type, good for 60 days at a time for 10 years. While I was(am) here in China I applied for and was granted a 30 day extention so that I did not have to leave China to get a few more sites in. However, now I'm concerned about whether or not my origional L type is still valid. Is the extention treated as a new visa? Or can I still come and go for the duration of my original L type?
Thanks!