[drcy]

I just looked at the close-up images, in particular the printing details, along with all the other images.

If the cardstock has all the signs of being old (smells musty, foxing, passes the blacklight test), I am confident it is original and authentic.
This isn't just from some general "feel" or "impression." I was looking for distinct printing and ink details in the close-up image. Plus I considered all the other images and evidence.

The funky staining made me wonder too at first. However, I don't think it's deceptive toning but water damage or staining it got sometime over the years.

This would be an item worthy of restoration and cleaning.