When adding a death date to a name heading that previously had an open date, should the former heading be added as 400 subfield $w nne?
No. It is LC policy that the subfield $w combination “nnea” should not be used in the LC/NAF for personal name headings when the only difference is an open date vs. a closed date. OCLC, at LC’s request, will be providing an RSS feed to libraries with notification of changed headings to be available at: http://www.oclc.org/rss/default.htm This service should help libraries identify what headings have been changed and facilitate local maintenance.