From the New York Public Library’s Acquisition Policy (1973):
Works of a Pornographic Nature
Pornography is defined as writings of an obscene or licentious character. The term, “works of pornographic nature,” is used here to include works judged pornographic by current standards and works formerly judged or considered to be pornographic.
3. Material sold in bookstores which specialized in “pornography for profit”
The third category of material does not appear in lists or catalogs, but is to be found in outlets or bookstores specializing in “pornography for profit.” Three or four times a year a member of the staff will be delegated to purchase samplings of books and periodicals at these outlets. Collection in this category will be on a selective basis.