The search index list at https://koha-community.org/manual/17.11/html/13_searching.html#koha-search-indexes doesn't mention the indexing of the 035 as other-control-number established in Bug 6499 (https://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=6499)
Added 035 to the manual
Fixed in newer versions of the manual: https://koha-community.org/manual/18.11/en/html/searching.html?highlight=indexes#indexes