I-130/I-797 need your help

[familybased]

Both my brother and I filed I-130 back to 1996 (F2B). INS received and proved our petitions on 06/07/1996. each of us got a receipt number (WAC) from INS and a few days later a case number was assigned by National Visa Center for each petition. I have kept all the documents including a cashed check and returned certified mail, which shows that INS received our applications on 06/07/1996. Till recently, I notice a problem about our priority date because the National Visa Center has started to process our immigration petitions. The priority date from NVC is 07/06/1996 instead of 06/07/1996. I contacted both NVC and INS help lines and got two different answers. NVC instructed me to follow their priority date. INS informed me to file on 06/07/1996. Have anyone run into this dilemma or can anyone tell me whether your priority date from NVC and on I-797 is identical? After waiting some many years for our priority date, we all understand that one-month difference can mean 4-5 months under F2B category. I really appreciate any advice.

Here is my I-797 information
Receipt Date: 06/07/1996
Priority Date: 06/07/1996
Notice Date: 08/02/1996

U.S. Postal Service:
Mailed out 06/04/1996
Delivered: 06/07/1996

Our I-797 WAC receipt number was written on the cashed check and dated 06/07/1996