Yeah, I have to agree, That's a litho Plate (or part of one) and it looks like it was for some kind of year book. I was in the Printing / Ink Making industry for over 25 years, I see Plates in my sleep. Never saw a year book Plate. It should be much bigger, the size of the paper it was printing. We took and cut our old used plates into small pieces and dump them into a metal 55g drum and sell them to the scrap metal man for cash. Maybe that is what you found seeing how it not what I would call a full plate.