I'm not sure I've correctly understood your case.. You are sure that your device is a Realtek, but that device is also imported in Mexico by a different brand/vendor. Is it right?

The "Generic Vendor" entry could be useful if the list of the (worldwide available) vendors was complete for each category of hardware. Otherwise, as indeed you have pointed out, some users could choose Generic Vendor just because the correct vendor is not in the list (instead of asking for the insertion of the missing vendor).

Otherwise we can add the "non-worldwide available" vendors in the list too.. perhaps in this case we could have some devices that have more than one brand/vendor (worldwide available and not). Anyway, I think we can use the VendorId:ProductId (PCI ID) code to identify one device. In this case the same product sold by different vendors (worldwide available and not) should have a different VendorId:ProductId (PCI ID) code (but perhaps this is not true).