I think they did have a way to annotate, but I'm not sure how. I've come across a couple of these as well, and in one, there were notes and comments in the margins, in a completely different font to the main text; in some places there were two or three different fonts with varying degrees of legibility and boldness. It was actually very annoying as I couldn't see how to easily get to a clean version of the text, and in some places it had gone all the way through and affected the legibility of the text on the other side.
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