Hi Michael,
I've written to the SA collector to encourage, actually urge, him to search the SAAF archives for documentary evidence that IWC Ref 2612s were purchased and used by the SAAF as navigation watches, and to send his SAAF Ref 2612/Mark 11 to Schaffhausen, along with the documentation, to legitimize this Mark 11.
He is, however, an executive of a multinational company and busy with his revenue generating activities. Collecting watches of the SA military is but an hobby. So, even if he succeeds in gaining access to the SAAF archives, he will do that in his spare time, and at his own pace.
Regarding the difference in the engravings between the SAAF Mark 11 from 1961 and his Ref 2612/Mark 11 from 1969, my comment is that the difference may mean something, or nothing. There is a 8 year gap between the two watches, and the task of engraving the case backs to affirm SAAF ownership, may have fallen into a different person/department, with a completely different engraving criteria. Also, the lack of any engravings in the Ref 2612 gave them more space to engrave the AFxxxx in a larger font.
BTW, there is also a marked difference in the case back engravings between the RAF Mark 11s from 1948 and 1952 (xxx/52).
AF9538 is not the only one known. It is one of two, although it is the only complete one extant, as far as we know. It is possible to see an image of the surviving twisted case back of the other one AF9229, in my posting earlier in this thread.
I realize that two is not a big number, but I venture to say that it may be big enough, if we consider the size of the SAAF, the total number of Mark 11s it purchased (guesstimation circa 200), and the fact that most were destroyed when they were decommissioned.
The research continues, to quote the celler.