Bulbasaur base set resistance printing error(?)

Hi guys

New to the forum as I knew this would be the place to come for expert knowledge on values, misprints etc.

I was looking through my old uncommons & commons today and by chance came across this base set bulbasaur which I thought was dirty by the resistance value. On closer inspection- it isnt dirt, the mark isnt raised and appears to be some sort of possible printing error perhaps. There is a sort of yellow and dark green crescent shape (see pics)

My question is-has anyone seen this on any other WoTC cards and is it worth anything more than a usual bulba would be? (Not much I know!)

Thanks!