Sometimes, someone will ask: "Why do you keep a copy of that book? You've got another one."
And that's true. The books in the Research Library have come from a variety of sources - from the libraries of retiring professionals, for example - and many of their books overlap. What doesn't overlap are the inscriptions and annotations, which turn a book into a unique archival document - the notes and inscriptions mean it's no longer a duplicate copy, but an addition to the archive. For an adventure in inscriptions and bookmarks, see "A First Archival Mystery of 2016".
But what about those "duplicate" copies - the earlier editions of a work, which has been superseded, for example? For instance, who needs DSM III, published as far back as 1980! (and sadly, the earliest edition we have) now that DSM 5 is out? DSM stands for the 'Diagnostic and Statistical Manual of Mental Disorders', and it has been published with regular updates and revisions by the American Psychiatric Association since 1952.
So why save an earlier edition?
Here is an email from Martin Manby of the University of Huddersfield about a book for which we have a number of editions, back to the second in 1942 (which is effectively the first edition, for reasons we needn't go in to here). There are many times when the superseded becomes absolutely essential:
"I recently undertook some research for which I needed to understand child care legislation for social workers as it applied in the period 1968 -1973. The standard text is: "Clarke Hall and Morrison on Children". I consulted two university libraries. Both of them had current editions, but neither had kept earlier ones. The PETT Archive was able to provide me with the 1971 edition within a few days.
1971 was the key date for my research. I needed to understand legal requirements for social workers in the period immediately following the implementation of the Children and Young Persons Act, 1969 and the Local Authorities Social Services Act, 1970; and also to understand the context in which social workers were delivering their services at this time of rapid change. The 1971 edition provided authoritative guidance on these issues.
P.S. The help and efficiency of the service provided by the PETT Archive was invaluable"
We don't generally lend books; but sometimes, when it is critical and when the circumstances warrant, we set the rule aside. Not everyone can get here, and the research that Martin Manby did will almost certainly have made a practical difference to someone else's life: and what more powerful reason can there be for saving 'unnecessary', 'duplicate' copies - which may not be unique in the scheme of things -, but which have been whipped off the shelves of hard-pressed libraries elsewhere, and utlimately sold for specialist retention in places like this.