Currently, when 264 ind. 2 is left empty, Koha won't show a label for the field in the OPAC. As quality of records might vary, it would be good to add a fallback to the XSLT that covers unknown and empty ind. 2 values. https://git.koha-community.org/Koha-community/Koha/src/commit/e7855c0c016e2d0047c077f7057b7f7c6ef41a80/koha-tmpl/intranet-tmpl/prog/en/xslt/MARC21slimUtils.xsl#L233