Yes, you right: the cupery stems from Friesland. See: http://www.genlias.nl/en/search.jsp
Cupery with 34 pages hits.
Alsum with 5 pages hits
Levey with 2 pages hits
Smits with 34 pages hits; this name is general for the Netherlands.
Dijkstra (spelling with ij, not y) with 34 pages hits.
Friesland has own genealogical sites: http://www.tresoar.nl/
Cupery hits from 1871 and on.
Alsum from 1814 some hits
Levey from 1853 and on
Smits from 1861 and on
Dijkstra from 1859 and on.