On my family tree book (in Dutch, so it's hard for me to read correctly) from Klaas Dankert (Danckert)who lives in St. Annaparochie, Netherlands, most names are cutoff at the right margin, so am missing full names on occasion. Most of my family came from St. Jacobiparochie, St. Annaparochie, and Vrouwenparochie, Province of Friesland Netherlands. It's possible some emigrated to countries other than Canada or the USA or lived elsewhere prior to the Netherlands, like you I've seen Danckerts in Germany, etc. I will look through the book when time and see what I find.
My tree descends from the "Danckert Tackes" tree, who was a ship merchant, fairly well to do, b. abt. 1625, Oudebildt zijl (believe St. Jacobiparochie, Netherlands), d. 21 Apr 1706. He married Feijck Clazes (?can't read), she was b. abt. 1630, died Mar 1692, dau of Claes Jans en Trijntje (her family name unreadable). Their children were Trijntje, Jan, Claes, Hendrick (Henry) and Dieuwcke.
Their child, Hendrick (Henry) Danckert, brewer/farmer, b.?(gedoopt) 1708 Oudebildt zijl (St. Jacobiparochie?), d. 1736. He married (missing first name?) family name Douwes (of Leeuwarden, and also 2 Aug 1708 he married Tiep...?(family name?).
Hendrick and his wife had four known children:
Fijke married Cornelis Beerts, son of Beert Reinders and Neeltje Cornelis Kuiken.
Hiltje married Jochum Cornelis Jansen.
Jeltje married Sibrandus Gerrijts Reijtsma
Trijntje married Jacob Douwes
You can "Google" Klaas Dankert" and bring up the family tree...see if you find any names you recognize.