On a recent epsiode they showed some books in Mr. Peterman's office and they were Reader's Digest consdensed books. That is the standard for dressing sets for TV shows. I think they are sold by the pound for just such uses.
Now that is not the kind of book Peterman would have. And it is a jarring note for a show that spared no expense or trouble. I can't think of any series that spent as much money and used as many sets and environments as Seinfeld. One of my favorite touches is where the steam is coming out of the manhole in the epsiode where Jerry has the footrace.
The Reader's Digest books show a lack of attention to detail that is not consistent with the rest of the show. I hope the people that did such a beautiful job 99% of the time realize that their work was appreciated.