Well, you asked whether we think they do that.
My answer is that, no, I do not think they do because I rather suspect that would be treading a legal line.
My answer is that, no, I do not think they do because they specifically say they do not.
My answer is that, no, I do not think they do because the potential ROI would be very low and the risk is very great.
My answer is that, no, I do not think they do because it would be very easy to be caught (dude, where's my notes?) and very hard to prevent being caught (having to proofread every page for notes rather than just scan the dang thing).
My answer is that, no, I do not think they do because the effort to store and cross-reference all titles that come in for perpetuity would be immense, and you'd also have to check cover, edition, footnote content, and ISBN on the back cover.
My answer is that, no, I do not think they do because of all the books they receive, probably no more than 5% are duplicates. People scan different things, and there are a lot of books out there.
So, no, I don't think they do.
