NACO: Imprint Dates
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Princeton University Cataloging Documentation

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Imprint dates

Give the imprint date as it appears on the bibliographic record for the work, except do not use brackets even if the bibliographic record would show the imprint date bracketed.
Include the copyright "c", question marks, hyphens, etc. If the imprint has multiple dates or open dates, record them.
Leave one space after an open date, before the subfield b delimiter.

If the imprint date is from a non-Gregorian calendar, record only the Gregorian equivalent without brackets.