So I did a little more research and I'm pretty sure that Tjerk is connected to the wrong Catherine Dederick. From the source on his page: "Tjerck, bap. at Saugerties 2 Oct. 1757, d. 25 Nov. 1832. He m. 3 Aug. 1784 Catharine Dederick, b. 23 June 1764, dau. of William Dederick and Christina Baer. She d. 7 Oct. 1835." The Catharine described is Diederick-4, but he is attached to Dederick-17, who seems to be a different person.