...
Books held by Schlesinger are periodically replaced; in most cases, this is due to the arrival of a gift copy in better condition, with more significant provenance, or other such factors. In order to replace an existing copy, rather than add the new item as a second copy, several steps must be taken. These instruction assume that there are two copies in hand (copy switching), though they can also be applied for to the replacement of lost books (copy replacement). Replacement is used for both throughout.
...