I have traveled to the US 3 times now within the past year, on the 2 previous trips, CPB stamped my passport for entry up to 6 months for which I stayed only 2 weeks each. On my 3rd trip in February, I was stamped for admittance for one month only, however something has come up that necessitates I stay an extra 3 weeks. Would this get me on the overstay list? I know you can stay between 90 and 180 days in the US on a B1/B2 visa, but given what was stamped on my passport, what is the best thing to do? Can I ignore it and stay?
The only thing to do would be to request an extension of your stay in the US if you qualify for one.
If the decision arrives prior to your departure date and it is negative you may have a very short time to leave the country before other legal measures may be taken by the USCIS.
A US visa is only for entry to the US, and the visa's expiration date only means the last day on which you can use the visa to enter the US. A visa has no bearing on your ability to stay in the US -- that is determined by the Admitted Until date on your I-94.
You are not guaranteed a certain duration when entering on a visitor visa. The immigration officer has discretion to give you as short a I-94 admission period as they feel is warranted by your circumstances.
There is no "overstay list". However, staying past the date on your I-94, even for a short time, has many negative consequences, including, but not limited to:
- The visa you used to enter this time is automatically void and cannot be used in the future
- You can only apply for US visas from your country of nationality for the rest of your life
- You cannot use the Visa Waiver Program for the rest of your life (if you have or will have a nationality that is covered by it)
- You may also have difficulty in getting US visas in the future, though how much of an effect it will have is impossible to predict
As @Karlson suggests, if you need to stay longer, you can apply for Extension of Status. You can stay while the application is pending, even if the I-94 is expired, as long as you filed (and the received) the application before your I-94 expires. Since it takes several months to process these applications currently, you should be gone long before they make a decision on your application, in which case their decision doesn't matter and you don't risk any automatic negative consequences (they may automatically deny the application after you leave because you no longer have any need to extend a status that you no longer have). The downside is that the application costs several hundred dollars. Also if you do this, remember to keep the receipt and any result of the Extension of Status application with you in the future, whenever you apply for a visa or enter the US, to prove to the officer that you did not overstay, that you left while an application was pending (because otherwise all they see on their computer is your Admitted Until date and the dates you actually entered and left; they do not see your EOS application).
If you are looking at a date written in your passport and you have no paper I-94 it might be worth looking at the Admit Until date on the (electronic) I-94, available from the CBP I-94 page, as it is possible the CBP officer just copied the date into your passport incorrectly. If the I-94 date is different then I believe it is the one that should apply, though you might want to print a copy of the record out and keep it with you on the (way-)off-chance someone cares. You have no choice but to file an extension if you want to remain beyond the date on the I-94.
If you have a visa or are visa-exempt (it should be one or the other if you previously got 6 months) note that if you are admitted as a B2 you will (almost) always get an automatic 6 months but for a B1 the officer needn't give you more than the time requested. Googling for a reference for the previous sentence finds this.