I need info on Mexico and brass error coins.

It has come to my attention that a few silver coins minted in the mid to late 1800's had some brass alloy coins produced in error.

I found a 1877 25 centavos that is brass and not silver.

Where do I look to research this?

I saw an EBay listing for a "brass" 1/4 real that was supposed to be copper. Graded by NGC.

Mine is a 1877 GoS 25 centavos with wear so I highly doubt a modern reproduction.

Thanks for any help.

Might look brass when actually silver ?