H1B Cap Exempt time limit

Dear Experts,

My employer had applied for a H1b visa in the year 2008 which was accepted but I never got the visa stamped nor traveled to USA ever. I checked with my employer and they say that I can still apply under the cap exempt category since my H1b was already approved earlier. However, they haven't been clear on what is the maximum time limit till when my earlier petition is cap exempt. I believe it is around 6 years in which case I will be able to apply under cap exempt category only till 2014 but which month - Apr? June? Oct? After this time I need to apply for a fresh visa without any cap exempt advantage. Can anyone of you please throw light as to till when can I apply for a new visa under cap exempt category. Thanks in advance.