EDTF Date - 046 - RDACataloging Examples
http://resourcedescriptionandaccess.blogspot.com/2015/09/edtf-date-046-rda-cataloging-examples.html
RDA Cataloging Examples of use of Extended Date Time Format (EDTF) in MARC 21 field 046 for Special Coded Dates in Resource Description and Access (RDA) Name Authority Records
When supplying dates in field 046, use the Extended Date Time Format (EDTF) schema in all cases except for centuries; supply dates using the pattern yyyy, yyyy-mm, or yyyy-mm-dd; always add subfield $2 edtf except after a century. The more consistent use of $2 edtf is based on a PCCLIST discussion suggestion to simplify the use of $2 (always use except for centuries).
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Regards
Salman Haider