Visa stamp is what u get on passport at the consulate. it has validity with certain expiry date, and can be used to enter USA anytime before that date, u have to have a valid stamp for entry to USA.
Now the other term visa refers to status and it is what ur status is when in USA. Normally ones status is what stamp one enters on like H1, H4 l1 b1 etc. The I-94 mentions that status and also gives the date till u can stay legally in the US on that status. these dates vary g, for H1/4 L1/2 these are usually till the visa stamp expiry date. For F1/J1 D/s (duration of stay). for B1/2 usually 6 mths from entry.
If u want to stay longer than the initial approved stay as in ur case Nov 2004 they have to file for extension of stay with USCIS. Upon approval most of the time they get a new I-94 (looks difft from the original) that authorises the stay till new date. Ur supposed to keep that I-94 with the old one in ur passport and surrender it at the time of departure at the airline.
Some poeple also change their status from one category to other and go thorogh similar process as above.
in other cases there are H1 transfers where u will get a new I-94 with new dates even though the old one is not expired.
In such cases u can use the old unexpired stamp with new approval notice and other supporting documents for travel without requiring a new stamp in the passport if traveling before expiry of stamp.
But for change of status(COS) and extension cases either the stamp is expired or is of the wrong category so you need to get a new stamp.
One thing u need a stamp only for travel not as proof of legal stay in USA. The I-94 is the document that needs to be current for legal stay, and governs what status u r in and how long u r allowed to stay. So if u change status or extend it u dont have to get the stamp till next time u travel if the approval comes with I-94 attached.
and file for extension following the date on the latest I-94. Last action overrides, all past ones.
