There are RPMs with three distinguishable mintmarks, but this isn't one. Rather I think that the copper plating has split and the underlying zinc core is starting to deteriorate.
"If you climb a good tree, you get a push." -----Ghanaian proverb
"The danger we all now face is distinguishing between what is authentic and what is performed." -----King Adz
Zinc Rot corrosion is eating away at the Zinc core underneath. It's Post Strike Damage ( PSD), meaning that the damage happened after it left the U.S. Mint. It's worth face value.
There can certainly be a D/D/D, even more than that, but yours is unfortunately not a RPM at all. Your coin is suffering from zinc rot, which plagued almost all of the 80s zinc coins.
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