I found your message on this site. I suppose we're related because my mother is (was) Pieternella Cornelia Maria Dekker. She was a daughter of Pieter Dekker en Janna Maria Klootwijk. Pieter Dekker was a son of Pieter Dekker and Pieternella Cornelia van Dalen.
I am very interested in all you found untill 1600!And maybe there are still gaps to fill?
I live in Papendrecht so maybe it's possile for me to help you. Can you send me a message?

Thank you very much
Annemarie Borst- van Mourik