You are referring to the so-called "Cape Naming" Register.
The copy found at the Cape Archives some 30 years ago covered the period Dec 1904 to Nov 1908. I enclose a scan of a typical page covering part of May/June 1907
The second entry in June (Gladwin) refers to a medal I sold on City Coins where the unit was altered from Eat Griqualand Field Force to Herschel Native Police.
Without the supporting Register copy page it would have been simply a defective medal.
There are records of well over 400 locally engraved/impressed SAGS and Cape GS medals and numerous cases of major changes on QSA's, etc.
From another source (the hand-written copy of the lost Issue Register for the CofGHGSMedal) it is clear that the local naming was done prior to Dec 1904 and even as late as 1912. However, registers are not available.
Yes, that was the one. City Coins Auction 58 featured the medal you mentioned. The description of lot 132 includes the statement: "The medal was skimmed in total, and rank name and unit reimpressed" (upside down). The City Coins description refers to Armstrong and Co. doing the work.
I obtained a copy of the "Cape Naming" Register at the Cape Archives in the early 1990's. As I recall the file was re-classified as "Not to be photocopied" afterwards. I do not have a File Reference Number and I to not know if the heading contained the names of the two firms involved (Seale and Armstrong & Co). I assume if a member well-versed in the ways of the Cape Archives can trace the relevant file, it can be photographed.
My other source is explained below
I got a copy as a thank-you present from my friend and medal-mentor, Frank Mitchell, some time before he passed away. It comprises just over 170 pages.
If any of you would like to copy ( I have an A-3/A-4 copier) or photograph these two documents, feel free to visit . However, let me know well in advance to confirm that the date fits in
The write up days:
Q.S.A. with bars Cape Colony and (copy bar) Defence of Mafeking to 21619 Pte. J. Morrison Marshall's Horse. With research roll, states Cape Colony bar which is struck through and Defence of Mafeking bar entitlement. Vendor has purchased a copy DOM bar from Dixons. Naming is correct and research shows in Remarks column N/N Pte. Mafeking Rly. Vols. N/N Nesbitt's Horse, 62 Aberdeen D.M.T. NOK Brother who lived in Cradock.
Cost is £1750. This price would be OK if the DoM clasp was original.