Bkmk
—good book on the mutiny—
'sz' at the end of a Dutch name from the 12th through 19th centuries often comes from the genitive abbreviation for "son of." 'Zoon' is abbreviated 'z' and the 's' before it come from the name immediately prior. It was very typical for such names to end in -s, as most were at times expressed in Latin.
My great-grandfather's name was Christianus in its Latin form, but was often rendered as 'Christiaan' in the familiar Dutch. (Underlyingly, the 'a' in 'Christianus', occurring as it did in an open syllable, was long. With the Latin male nominative ending (-us), it therefore would typically have been rendered via the doubled 'aa'.
Cornelis is a typical Dutch name in the 12th through 20th centuries. A trailing 'z' is so conspicuous to a Dutch eye, that it would have been clear that it stood in place of 'zoon' as it did in many other neighboring European languages, as in Christianson, Josephson, etc.