Well from a back yard rookie point of view.....That sheet is too nice, with WAY to evenly layed browning. I would have the 4 X's tested to check the age of the ink. If it's about a few years old then bingo! Of course, they could have a pen from the 60's that they are using to show aged ink. My other trick is smell. I have smelled many of these so called original invoices and build sheets. The original ones have this certain smell of age, and mildew, and must. And if I don't get that smell, I would think twice. But ya gotta have the nose for it. When I see those guys with documentation schrink wrapped in plastic. I have them cut it open so I can smell it. Just say'in, that's what I have done in the past. And it works pretty well. It is hard to get that aged paper smell. Very close to an old newspaper, but not quite. Anyway, looks too good to me...Danny