Which date is my last valid date, H-1B approval or I-94?

My H-1B status is supposed to be valid until 9/30/06 as shown in the Approval Notice. I went back to China in February. I got an H-1B VISA on March 7 to come back to the USA. The expiration date on the VISA is June 7. Moreover, it also says June 7 on my I-94. I don't know which one is the last valid date. Do I need to have the date on my I-94 changed to 9/30/06?
Thanks a lot.