When entering the esp@cenet service you are offered a choice of several databases. These databases differ in their data coverage. When searching in "worldwide patents", you will cover the largest range of documents. By searching in "Belgian patents", you will only cover the last two publication years of Belgian patent documents.
Do not expect to cover the whole state-of-the-art by searching in national Patents only.
Databases available on esp@cenet® have also some limitations in the number and the quality of fields accessible that should be considered when drawing conclusions from the result of a search.
Commercial patent databases usually offer extra value, by the number of fields you can access, and due to the content of the abstract that has been rewritten to facilitate easieraccess to the document by keyword searches.
To sum up, a patent database user should always be aware of the content of the database he is using and know the limitations of the fields.