See also (used for reference only);
- https://www.digibron.nl/viewer/collectie/Digibron/offset/9/zoekwoord/melkbus/id/tag:RD.nl,20020703:newsml_5f015eca146923feac8dcc69d43a31f6
- https://www.dekrantvantoen.nl/vw/article.do?v2=true&id=DVHN-20020704-DM01015005
- https://rkd.nl/nl/explore/artists/231525

Additional links (not used) via
http://www.staphorstinbeeld.nl/index.php/component/advportfoliopro/project/11-kunst/101-de-laatste-melkbus-nieuw

Also,
- One source supposedly made a typo "C. van Heck"
https://standbeelden.vanderkrogt.net/object.php?record=OV19ad
- One source supposedly assumed "E. van Heck" was "Elsje van Heck"
https://edepot.wur.nl/152189
see
https://www.elsjevanheck.nl/elsje-van-heck/
(which I personally assume is the person it refers to)