This
1970 Topps #670 Ron Santo shall forevermore be known as
'Ron Splotcho.' Check out the lower left corner of the white bordered box. The first card is the 'normal' version and the other three have a large, dark splotch in that grey area, running into "Ron." It doesn't affect the white outline of the box at all, but it seems to go hand in hand with the darkened area of dirt in that same area...
1970santosplotch.jpg
Here's a better/larger representation...
3258095__07514.1641919896.jpg
They're very easy to find, so not much of a rarity.