July 13, 1863 was a Monday, so that offers a clue. My guess is the newspaper you referred to reprinted an article word for word from another newspaper. This was a very common practice, and can be very confusing sometimes because the papers doing the re-printing more often than not offered no context or original date of publishing for the reprint. They generally would include the name of the newspaper at the beginning or end of the re-print and that was all there would be.