Currently (04 Sep 2016) Diederik is connected to Katharina van Wyk as per SAG? but Johanna Catharina van Wyk , her mother's inventory http://databases.tanap.net/mooc/main_article.cfm?id=MOOC8%2F6%2E109a by 8 June 1746 makes no mention of a surviving Catharina van Wijk at the time.
The Catharina van Wijk who was married to Diederik Koekemoer died some time after (by 19 January 1747) as can be seen on her inventory http://databases.tanap.net/mooc/main_article.cfm?id=MOOC8%2F6%2E114
Both Richard Ball http://www.ballfamilyrecords.co.uk/kfp/I196.html and The First Fifty Years Project http://www.e-family.co.za/ffy/g9/p9201.htm have this Catharina van Wyk, a2b1c3 Catharina van Wijk as Diederik's spouse.
Regards,
Dirk