This is only the second time I think I have ever found one of these, and I've scoured thousands of coins from this date. They are very scarce.
This one, however, does not match die markers, so seems like it could be a different stage. This is one of the odd RPMs that gets stronger as the die ages, but I am thinking this would be a stage D as the secondary mint mark starts softening out and fading as the die got older still.
1956 D & D
Lincoln Wheat cent - RPM-018


