The 'numbering' as originally imported should read as originally created and applied by the various researchers in the previous century. Their work has then been imported via GEDCOM into WikiTree (and other sites).
The numbering system dates from long before the computer age. To us South Africans (or expats) the system is only indicative, not leading. And the interesting thing is when they don't match up - the algorithm wins. There were many mistakes made, especially in the genealogical lines of the 19th century. For more information see here: "To people not familiar with the system, it can be both unsightly and confusing. It has also been criticized for not including the offspring of female descendants. It must be remembered that the theory is that the female marries into another family and that her offspring, having the surname of her husband’s family, will appear in the new families genealogical or descendants chart. Of course if the new family hasn't been recorded yet, the information about her descendants is lost, which is a problem. It must also be remembered that when publishing a compilation genealogy, such as de Villiers Pama or SA Genealogies, if the publishers were to include the offspring of females within her family and then repeat it for the descendants of her husband’s family, these volumes would have twice as many pages or there would be twice as many volumes. a1b1c3d5[e1][f2] etc. with the d5 being the female and her children, grandchildren and other descendants being enclosed in square brackets. Another criticism is that it can only be used in a settler community such as South Africa where the first of the family can be identified as “a1″, the stamouer (progenitor). The system makes no sense in old communities such as in Europe where one cannot talk of a ‘stamouer’. There is of course one other consideration and that is that the SA genealogical number because of its combination of alpha numeric numbers is much shorter than overseas numbering systems that use roman numerals to fit people into the family. The problem is of course what happens when we pass the 27th Z generation."