Thanks for the info! For the record, here's what I have:
James Swinnerton, original art, Mr. Jack strip, 1/28/1920, signed by artist, engraving order and postage attached.
F. Opper, original art, "The Judge and the Major," 5/1/20, signed by artist, engraving order attached.
F. Opper, original art, "The Munitions Plant Blew Up!," 6/2/20, signed by artist, engraving order attached.
Items were acquired some years ago at Berman's Auction Gallery in Dover NJ, in a box with misc. old printed newspaper comics. I no longer have the record of the purchase.