I was cleaning the trunk in my 70 Supreme Convertible when I came across this stamped in the back near the bumper. Anyone know what it stands for?

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I have seen it before but not sure what it is.

 

My 72 has stamped codes on all the metal work. That stamping is the die number the part was created from IIRC. I have the exact same stamping in my trunk too. But underneath there is also a stamped ordinal production date.