This is a tracking category.It is used to build and maintain lists of pages—primarily for the sake of the lists themselves and their use in article and category maintenance. It is not part of the encyclopedia's categorization scheme.
This is a tracking category for CS1 citations that use the Accept-this-as-written markup (or the parameter) to indicate that although the given ISBN is malformed it is indeed printed on the work. These malformed ISBNs can still be looked up via Special:BookSources in the usual way despite the prominent warning -- it just means that fewer Find this book links will actually work (most libraries will work, most dotcoms won't).
This is not an error category and pages in this category should be "fixed" only if the special markup has been misused (see Help:CS1 errors#bad isbn, which describes the only valid use of this parameter).
Articles are listed in this category when a cs1|2 template uses the markup regardless of the validity of the ISBN. Pages in this category should only be added by Module:Citation/CS1.