Re-entry into China with a Previous (but valid) Visa?

Hey everyone,

I studied abroad last summer in Shanghai and thus received a multiple entry, F type that allows me to stay up to 90 days in China at a time. It was issued on May 17, 2012, and it doesn't expire until May 17, 2013.

I plan to go back to China this summer to visit friends and do a little traveling. Would I be allowed to return to China on my current one, as long as I enter before May 17, 2013? Would the Chinese government question this and possible deny me entry into the country? My original plan was to just apply for a new one, but I was told by someone that I cannot apply for a new one as long as my old visa is still valid.

I really want to go to China this summer, and I am just trying to determine my safest route for being able to enter the country. Thank you so much for your time, and I am looking forward to anyone's advice.