INS and DOS
chaudhar,
INS and DOS are two different deparments till now. They will get under one head "Home Land Securtiy" very soon.
I-94 is issued by INS and the re-validated stamp is issued by DOS. When you entered US last time, the immigration officer must have put an expiry date on I-94. But if you get a new H1 after your last entry then you find a new 1-94 attached with the letter (I-797a) sent by INS. The expiry date on the new H1 I-94 superceeds the old expiry date on the old I-94.
Hence to my knowledge DOS will not apply any new expiry date on the I-94. You should be OK with what you have.
Thanks.