Hi VLD549!

Thanks for asking! This edit is part of a much larger project updating the map with all (historic) islet names and historic names of waterways still present. The Smeersloot is located roughly at the location where it is located through extensive research. Unfortunately the main source used is not available online. It is a book published in 2019 which features two maps with field names. It can be accessed through the National Library of the Netherlands.

Fortunately, the smeersloot is also mentioned on this map:
https://www.regionaalarchiefalkmaar.nl/collecties/beelden/beelden-2/detail/94467d52-4692-84b5-e083-fb69ed2311f1/media/57ef7efd-e490-248d-e123-84007b997efd?mode=detail&view=horizontal&q=broek%20op%20langedijk&rows=1&page=3&fq%5B%5D=search_s_uiterlijke_vorm:%22Kaart%22&filterAction.

Let me know if you need assistance in understanding the map (since it's in Dutch).

Best wishes! And thanks again for your interest!