That’s interesting, Peter. The house on Waldo that was owned by Bowie Dash (and later Zambetti) certainly had the look of a “gardener’s cottage.” The “Gardener’s Cottage” is also referenced in the Historical Guide to the City of New York here: https://archive.org/details/historicalguide00yorkgoog/page/n225/mode/2up
For anyone who hasn’t checked out that book, I would highly recommend it as a local history resource. It includes maps for self-guided walking tours such as the one below. 22 on the map is the Upper Cortlandt mansion house and number 21 is the “Gardener’s Cottage.”
Although according to the blurb in the book, the cottage was near 238th and Greystone, so yeah, more research needed to really figure it out what exactly was the “gardener’s cottage.”
Tom, would you mind sending a link to the Dash property that you found on the Hudson?