I didn't have the advantage of a close up but was willing to bet it was authentic. That weathering/paper fading on the back alone is very, very hard to replicate. It's layered in it's fading meaning it appears to have been stored between other period documents for a long period of time. The acids from the papers more than likely created it and not light. The printed lettering at top also appeared to show or bleed through just a little which told me it wasn't made from two substrates. From the close up I could see here it appeared to not have any halftone dot for sure but would have loved to have seen a closer pic of the printing. Hard to replicate that early printing. Most one and two color work was Lithography or Letterpress back in the day and the surface is unmistakable in it's finish and texture. It's a great piece for sure.