Anyone could bring a bookplate to a reading to have it signed. But I have never seen one, for the record. I think it's premature to assume it was done by a forger. The more I look at it, the more it looks like '73-'75 to me (per Ski's note and my copies of SoNN, Burning and Love is a Dog). This would be consistent with his use of thicker felt tip pens during that time and would be consistent with what he's wearing, his apparent age in the photo and the green Dodge (I believe) that looks to be a '69 or '70 and appears to be a few years old.