The 3-volume Catalogue of the Papers of James Boswell is an indispensable work of reference for any Boswell enthusiast. It contains fairly detailed descriptions of all the items in the Yale Boswell collection that were available at the time of publication, including papers that have not (yet) been published in any other format.
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Sadly, none of the primary contributors to the catalogue, including the main author, Mrs Pottle, lived to see the work published. When it was finally published in 1993, Mrs Pottle had been dead for little under a year, her husband for six years and Claude C. Abbott for 22 years.
The complete catalogue is not difficult to find, but it is expensive and seldom available for less than £220 in used condition via AbeBooks.