My in-laws just got here. Their visas are valid for only 3 months, but they got an I94 card valid for 6 months. It is the duration of I94 that matters here.
Again, we are talking about two different issues here. One is visa stamps (the visa on our passport). The other is visa status. Visa stamp is for entering the U.S. This has to occur before the expiration date. The visa status is determined by the INS office when entering. Good luck.
For 中信辦理免麵簽, if your parents go back to China, as long as their current visas have not been expired over 1 year, they can go to the Bank for visa application.