Queen Victoria died in January 1901 while the war raged on. Her son and successor, King Edward the VII, decided he wanted to award a campaign medal to mark the war that was ongoing when he came to the throne.
To avoid the expense and complexity of issuing clasps for distinct actions, of which there were many small ones during 1901 and 1902, it was decided to just use date clasps of which there are two; South Africa 1901 and South Africa 1902.
To qualify for a KSA a recipient had to be serving in South Africa in 1902 and have spent 18 months on war service in South Africa. Service could be broken, for instance wounded or debilitated soldiers sent to the UK for convalescence and then returning.
The KSA was always issued with a clasp, except to nurses and civilians. It is most commonly found with the two date clasps, to have one clasp is rare and always needs to be verified on the medal rolls. The KSA was almost always issued complete. In some circumstances where a man had been issued the dates clasps off a QSA Supplementary Roll then a KSA with no clasps was issued.