426 Hemi decoding

I have a RM21J9C stamped on the engine pad with the 6 numbers. I've done a lot of research and can't find where roadrunners were assembled at the Jefferson plant. Has anyone ran across this or know where I can go to find out why I have a C instead of an A code.

Thanks,

Robbie

The C may be a poorly stamped G.

Agree with Barry probably a G for St. Louis plant.
Matt