I checked a mint "23" in 2nd Class in my collection, and discovered the marks you highlighted above to have been filed & finished down. In other words, the "slots" were filled, and the finishing file marks are perpendicular to the seam, but just in the inner corners. I would hypothesize with the marks on yours, Rick, the solder was either removed or wore away. Wouldn't those inner corners be the most difficult to (hand?) solder anyway? I am sure there were finishing files that fit those inner corners perfectly, thereby hastening the final hand finishing process, but these are just hypotheses, gentlemen. . . obverse: [attachmentid=8983] reverse: [attachmentid=8984]