The buoys are moved quite often due to shifting sands. There is an official dataset (https://data.overheid.nl/dataset/2c5f6817-d902-4123-9b1d-103a0a484979) with positions and other data of the buoys which is updated with the BaZ (https://www.defensie.nl/onderwerpen/berichten-aan-zeevarenden). I updated the buoys based on this data, see https://github.com/quantenschaum/mapping/