It would be erroneous to limit admixture to 1652 - 1834. Admixture is more correctly dated back to around 200 BCE - 450 CE in the first instance, then 450 CE - 1652 CE, then 1652 - 1828, then 1828 - 1870, then 1860 - 1910.
These represent:
1) The first wave of herder culture migration to the trans-Limpopo-Shashe region. These are the forebears of the Khoe/Khoi who were an admixture of Cushite, Nilotic, sub-Saharan, Hadzabe and Sandawe roots who then mixed with the Tshua, and Khwe San peoples in the territory between the Zambezi and Limpopo-Shashe Confluence. The Tshua and Khwe were the northernmost of the many San aboriginal peoples of Southern Africa residing in what is called Angola, Zambia, Zimbabwe, Botswana and Namibia today. The Khoe/Khoi would fan out in new migrations north, west, east and south both assimilation with other migrations and have a distinct identity of their own. They reached the Eastern Cape according to archaeological evidence around 650 CE along with other migrants of Kalundu culture according to archaeological evidence. Both settled among the southern San aboriginal societies in the region. The Khoe and proto-Xhosa (Kalundu descendants) moved southwards together into the Western Cape, and the Khoe/Khoi further into the Southwestern Cape by 1100 CE. The San got displaced by herder and farmer cultures into the less hospitable Central Cape. The earliest admixtures took place during these times. The San aboriginal people and the Khoe migrants became the first and second of three Foundation Peoples in the foundational phase of the peopling of the region from Zimbabwe to Agulhas.
2) By 100 CE the emergent Khoe/Khoi were joined by Kulundu migrant cultures coming from Angola in a drift from West Africa (sub-Saharan) and over the next 350 years, drifts of Nkope cultures from Central Africa and Kwale cultures from East Africa (sub-Saharan & Nilotic) They were Bantu language speakers, farmers and metallurgists. There was admixture between these migrants and both the emergent Khoe/Khoi as well as with the San. This resulted in the emergence of the third Foundation people culture which came to be called the Kalanga. The Kalanga established themselves in Botswana, Zimbabwe and the northern areas of South Africa with some sub-cultures moving south-easterly.
3) From 450 CE to 1100 CE the Ziwa and Zizho cultures that birthed Kalanga culture saw the first emergence of the age of pastoral Kingdoms in Southern Africa - staring with Mapungubwe, This was followed by Great Zimbabwe, Thulamela, Butua/Khami, Mutapa and the Rozvi Empire. These kingdoms became magnets for further migrations particularly from Nkope and Kwale culures from Zambia, Congo, Tanzania and Mozambique. Particularly during the revolutionary climate of the Mtupa, Kingdom, the Rozvi Empire and the Tsonga kingdoms this gave birth to a new wave of kingdom formations in South Africa. All of this while in South Africa circular migrations were occurring with movements in Gauteng, Botswana, Northern Cape and Lesotho while strong pastoral societies developed south of the Limpopo. Trade had developed with China, Arabia and India by 700 CE already with gold and ivory exported through Sofala and Kilwa and glass beads and porcelain first arriving in South Africa. Semitic influences and admixture had filtered down these trading roots on the East African coast with the emergence of the Lemba people among Kalanga rooted communities. Another phenomenon was the emergence of the Bokoni.
4) From 1100 CE - 1652 further internal and external migrations occurred while processes of segmentation and differentiation and diversification saw every new communities and kingdom formations getting established. In the area of Eswatini, Mpumalanga and KZN of today. there was an admixture rooted in San (Twa), Khoe/Khoi, Bokoni, Hlubi, Tembe, Tsonga, Rozvi (maMbo/eMbo) that came together giving rise to the Ndwane, Ndwandwe, Mthethwa, Zulu and other formations. Only in the early 19th century when a soldier from the small Zulu clan, in the Mthethwa army, Tshaka, repeated the revolution of the Rozvi by uniting the many eastern South African societies was the modern Zulu Kingdom established. They were not alien migrants from the north but had emerged over 1200 years in the region having multiple roots. These drifted down to the Eastern Cape by the 13th to 14th centuries and continued to do so in the 15th and 16th centuries. There they engaged with the Xhosa and Thembu forebears and Khoe who had already been in the region for 800 years. Over that long period it is inconceivable that there was no admixture, and this is borne out by dna results. Both in the European engagement with the Mutapa-Tembe-Tsonga in Mozambique through the slave trade from 1500 - 1652 and during the 1600 - 1652 period with the huge European traffic through Table Bay (0ver 1000 Dutch ships alone and up to 600 English, French, Portuguese, Danish ships) the first European admixtures with the already diverse African indigenous admixture was introduced. (It is inconceivable that with records showing layovers of ships averaging three weeks at a time, as well as a number of shipwrecks at east two where large numbers of Europeans stayed for between 4 months and one year that no admixture occurred)
5) The slavery period did not end in 1834 (or 1838) as thousands of mainly African enslaved continued to pour into the Cape from 1828 until around 1870, known as the "Prize Slaves" or "Liberated Africans". They were braded and had to work out a 14 year apprenticeship, later reduced to 5 years. They were placed in employment strictly within 20 miles of Cape Town. This again contributed greatly to the admixture in the Cape population. These Africans were from both the West and East Coast of Africa and inland as far as Zimbabwe, Zamia, Congo and Malawi as well as Madagascar. This substantially increased the numbers of enslaved at the Cape outside of the 1838 figure as "Prize Slaves" were not counted as part of the formal reparations to farmers exercise. What also has to be factored in are those enslaved moved from the Cape via the Great Trek and the large-scale enslavement between 1838 and 1885 in the Boer Republics.
6) Then finally in the period 1860 - 1910 the phenomenon kicked in of the "Indentured Labour" era with mass migration from St Helena, China, British India and British Africa. The figures were in the tens of thousands and represented a major influence of admixture. Alongside this was free migration too from a range of places from all the continents in the world. The mass influx of British troops starting in 1806 and reaching its zenith in the second Anglo-Boer War when troops from other British colonies were also part of the armed forces eg: Australian Aborigines who were abandoned in SA after the war. On the Boer side Russians of mixed heritage, Germans and Irish poured in. The gold and diamond rushes before the Boer wars and the busy Cape Town docks with its influx of Caribbean and African-Americans... and the Turkish migrations and assimilation into the Cape Muslim communities.... all of this contributed to admixture in South Africa.
Thus I would caution about too narrow an approach to the subject.
I also caution about the language of genealogical genetics which sometimes veers way off science and scientific language. For instance, there is no such thing as Khoisan dna and Bantu dna. There are dna haplogroup markers that can be associate with San and Khoe peoples and with the over 7000 ethnicities who have languages that broadly fit into the diverse family of Bantu-Languages. It is more scientific to refer to Southern African dna markers, East African dna-markers both od whom have San and Khoe associations in 9 different countries, and to sub-Sahaan dna markers, North African dna markers, Nilotic dna markers, Cushite dna markers. The point is that DNA is not ethnic orientated or race orientated, as notions and associations on these have been constantly changing over time. Hence it is regions where these thousands of variations of Haplogroups are most prominent that defines them and their age. There has been much abuse within the commercial genetic-genealogical arena of what dana can and cannot tell us. Also any person doing a dna test rougly only gets a result of up to 50% of their genetic ancestry. Siblings for instance can get variations in their results.
This is an arena where we must avoid being emphatic and really come to grips with what DNA knowledge can assist us with and what it cannot assist with, and in so doing we need to set aside the "race" and "ethnicity" paradigms. We also must distinguish the vast difference involved in what constitutes "identity" and "human experiences" and what knowing one's ancient genetic roots can tell us. This is particularly important in the sensitivities stakes in South African human relations and the different consciousnesses that people carry.
This is just my two-cents worth of contribution to discussion.
