I have been to the USA under a B1/B2 visa previously, but then it was stamped on the page opposite to the one with the visa, where b2 was written and the deadline for exit was stamped.
The next time when I entered with a B1/B2, the stamp was put halfway across the page opposite the visa and halfway right over the visa, where B1 was written and the deadline for exit was stamped.
Does this mean anything? The visa is marked M, which I suppose means multiple-entry, and it still has a few years of validity remaining. Is this still the case now that it has been stamped across? Is there any way I can verify the validity of my visa?