stallzer - In case you weren't aware, your bottom 24c stamp is the "Scratch Under A" variety.
It has a Scott catalog listing, I believe under 70, 78, and probably other numbers for the stamp.
I "think" this link below will not be behind a paywall since its an old Chronicle article.
August 1991, Whole Number 151.
Article: Discovery of a New Plate Variety on the 1867 Grilled Issue:
"Scratch under 'A' of 'POSTAGE'" on the 24¢ "F" Grill, Scott No. 99
Author(s): Jerome S. Wagshal
https://chronicle.uspcs.org/pdf/Chr...51/17821.pdfI have trained my eye to look for these through the years. I have not found many, although I have discovered a few. Now yours. They aren't super common.