I've found a rather interesting grave in eGGSA's Gravestones in South Africa collection:
http://www.eggsa.org/library/main.php?g2_itemId=1453497
The inscription reads:
Sarah Ann Cory
Born 1812
Died October 1896
Beloved Mother Of
Mrs A. Stilwell
This is quite clearly a mistake. The Mrs A. Stilwell is the wife of Ablort Morgan Stilwell i.e. Sarah Stilwell.
"South Africa, Cape Province, Civil Deaths, 1895-1972," database with images, FamilySearch (https://familysearch.org/pal:/MM9.3.1/TH-1-9720-27620-58?cc=1779109 : 20 August 2015), 1896 > Queenstown > image 335 of 456; National Archives, Pretoria.
The name Sarah Ann Cory appears to be a concatenation of the names of both of William George Cory, SV/PROG 's wives i.e. Sarah Cory, SM and Mary Ann Cory.
The inscription appears incredibly clear, considering it's age, could this mistake have been made during restoration of the inscription? If so, is it known when (and by whom) it was restored?