This is an administrative category, used for maintenance of the Wikipedia project. It is not part of the encyclopedia and contains non-article pages, or groups articles by status rather than subject. Do not include this category in content categories (except for eponymous maintenance categories).

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This category is triggered if something other than a purely numerical value is entered in the date field of a language infobox. (Note that this does not happen if a merely unlikely date is entered.) An invalid input affects the display of the infobox as well as its ability to detect obsolete data.

Entering 'NA' or 'no date' in the date field triggers a subcategory. Though it does not cause any problems with display, it does prevent the obsolescence calculation.