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The original bib was for a paperback edition that should have been on the hc record to begin with. When copy was added, added to a non pcc pbk record, rather than bring in appropriate record. This was also true in the case of test case #3–I think we need to address this at the point of acquisition, rather than at cataloging. I think this would look something like:
If ISBN pulls up copy with edition statement "1st pbk. ed." or variant, and is not pcc, search by title to see if there is a pcc bib for the hc and if all else is the same, add 020 for pbk isbn and bring that record in.
Similarly, if adding new copy and find already existing copy, barring explicit instructions to add as c.2, set aside for the Curator, who can then decide if it is a replacement copy/added copy or for book sale.