A new guy, WELCOME!, is and in after an hour of no action on his question.

RM21M9A257118 was probably "built" Wednesday, 4/9/69 .....

What's your EAD?
What's the date on your "K"-frame?

What's your real question? You have your fender tag decoded.
Want to know the social security numbers of the UAW employees that built your car?