Thread:Support/Special:PrefixIndex/MediaWiki:Sp-translate-data- incomplete?

I have looked for the files for cy MediaWiki:Sp-translate-data-MagicWords/cy and MediaWiki:Sp-translate-data-Namespaces/cy in the category Special:PrefixIndex/MediaWiki:Sp-translate-data-. The files themselves don't appear to exist, although some Magic Words and the namespaces were localised to cy a long time ago. Why would this be?