Sidenote: afaik, "Van Vlack" is not a "Dutch" name.

Inappropriately adding the "Van" (which in Dutch is written with a lowercase v) is typically something Americans of Dutch origin did to make their name sound more interesting to Americans.

But for those looking to process Dutch names (or other cultures with similar construct), those names are sorted by the part behind the "van", i.e., "Jan van den Brink" (yes, it gets more complicated) will expect to find his name under "B".