1746 - Roelof Couvenhoven witnessed Jan Schenck's will (if trancription of a primary source was accurate & accurately included in the profile for Jan).
Most frequently found reference in search of columbia.edu library is van Couwenhoven. (just one hit with "K" - without the van - from 1850s).
I think for Jan's wife Sarah, it should be van Couwenhoven, but I couldn't find a reference to her specifically.