Looks like a scratch to me. Others more familiar with plate flaws and 1st issue revenues will know better than me if it's a new discovery. However, I looked through some back issues of The American Revenuer
to see if it had been noted previously, and came across this info which may be useful. From the October 1997 issue, Anthony Giacomelli's article "Cracked Plates versus Plate Scratches":
Beware when acquiring the so-called cracked plate stamps. They are often misdescribed scratches. See if there is a depression in the back of the stamp corresponding with a line of color on the front. Look for the raised ridge of paper at the line of color on the face of the stamp. Examine the flaw with a moderate powered magnifier. A scratch is fairly straight and smooth edged while a crack will be more erratic and jagged.