Datapoint Afrikaans/Proportion of native speakers

If I assume the 2001 Census results for number of people for whom Afrikaans is the language most used at home to approximately coincide with number of native speakers of Afrikaans (approx. 6 million speakers), and combine this with Grebe's (cited in Hinskens 2009) observation that the Census 2001 mentions there to be 16.3 million L1 and L2 speakers of Afrikaans, this means that in 2001 supposedly 38 procent of Afrikaans speakers was a native speaker of the language.