https://www.epo.org/en/service-support/faq/searching-patents/open-patent-services/search-queries-tips-and-tricks/when-i
When I use the bibliographic search request, why does a "published before" type of CQL query deliver documents that do not have any publication date at all?
Currently, if the publication date is unknown, the system stores a value "0000-00-00", as a date is mandatory. Thus a CQL query should be extended with an additional condition (pd > 00000000) in order to exclude documents without a publication date.
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