For purchased items, invoices have been retained since the late ninteenth century. If required, we can check these to gain information on the provenance of an item. Various aids to dating early printed editions have been published. The date given in each entry of the Catalogue of Printed Music to 1980 is the date of issue of the particular copy being catalogued, so far as can be ascertained. Firm date supplied from other source of information, whether internal or external.
Date appears in watermark.
Probable date - actual date may be the year before or after. Each volume of the Catalogue of Printed Music to 1980 contains an introduction giving further information on the cataloguing conventions followed, and on the arrangement of entries within the volume. In addition, provenance information can often be found in the catalogues . The Catalogue of Additions and Manuscripts Online Catalogue generally include fuller provenance information than the Hughes-Hughes and Willetts catalogues. They also provide an overview of the makeup of any one volume and an overview of the contents of larger collections.