I could be wrong, but I thought clashes only showed on the field, since Lincolns head would actually be incuse on the die.
Of course. You asked a very reasonable question and was one I should have tried to better address. While correct about the head being a low point on the die, this specific area doesn't show that much relief, plus is protected from polishing, etc. Between the two this likely explains why this is fairly common and often shows on coins displaying no field clashing.
Knowledge... ...I get awesome magnification lenses for .50/1.00 from old cameras/camcorders found at flea markets.