I'm a born Franck (different name now), my Franck family hails from Latvia.
I have been follwing your posts around the net today :) ... and in one it says something about "Courland", which "is the historically distinct area of modern day Latvia bounded by the Baltic Sea to the west, Lithuania to the south and the Dvina River (now Daugava) to the North"...
Something is not known in our family and the name "von Pfeilitzer gen. Franck" seems to give a clue.
Maybe we have some missing puzzles to share...
I saw your email on another board, so I will contact you later.