Is the Dutch translation incomplete?
You can try importing the translation file again; it is possible that the connection timed out and that some of the translations were not inserted.

However, if you check the .po file and you can't find the translations of those strings - it means that whoever was translating the terms did not finish them all.

You can translate missing terms yourself within Drupal at admin/config/regional/translate/translate or download Poedit and contribute translations back here.