The Biodiversity Heritage Library (BHL) is an open access digital library that aggregates digitized monographs, journal volumes, and archival materials from hundreds of different contributors. In some cases, a consecutive series of journal volumes are available, but in other cases there are gaps in coverage. With the metadata available it is difficult, if not impossible, to accurately identify gaps in coverage.  Identifying what is available is easy; identifying what is missing (the gaps) is hard.
These gaps in coverage occur for a variety of reasons: the volumes were not available for digitization due to contributor holdings or condition of the materials, or copyright restrictions prevented BHL from including the volumes in its open access repository. In order to more accurately present these coverage gaps, BHL followed guideline 6.4.6 (pg.17) in "NISO RP-9-2014, KBART Phase II Recommended Practice" where "A title should be listed twice if there is a coverage gap of greater than or equal to 12 months, with only the coverage field changing.”
The NISO KBART Standing Committee reviewed BHL’s KBART data file in 2020 and recommended each volume be listed individually. BHL’s KBART file contains many redundancies, but guarantees that each volume that is held in the collection is represented accurately. Therefore, when a new volume of a title is added to BHL’s collection, a new item (row) is added to the KBART file for that title. From the options listed in the BHL KBART Documentation, the decision was made to elect option 2 as the best method to provide holdings data in BHL’s KBART file.