What's the importance of the title list that
appears on the inverse of some dust jackets?

The title list and the number that appears at the top of many lists ("Which of these XXX outstanding books...") is extemely useful for dating the printing of that dust jacket, and thus for helping to determine if a dust jacket is a dating match for the book it's on. This is especially important in dealing with first editions.

This title list, as well as the one that appears at the back of many book blocks, was revised semi-annually in the spring and fall reflecting that season's current catalog (although January titles often appeared with the previous fall's lists).

For more information, as well as for instructions on how to use these lists to date books and dust jackets from 1925 to 1970, see Barry Neavill's Modern Library Dating Key article.

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