I have a two part question about a first printing Special Printing

I have an O57s, a 1 cent State Specimen with what appears to be a drop or splatter of ink on the left side of the value numeral. Close magnifacation shows some additional specks of ink on the E of ONE. The print doesn't look like soupy ink ( too much solvent in the mix ) so how would there be dripping ink near a freshly printed sheet?

There are also a couple of owner's marks on the back, one a small stamp and the other a couple of painted on letters, I think. When was it common practice to stamp a stamp with owner's marks?