I have now obtained copies of the two volumes of the KSA medal Roll for the Imperial Yeomanry available to download free from the National Archives web site as very large pdf files (WO 100/356 Vol 1 147MB & WO 100/357 Vol II 114MB).
Sgt Robertson appears in Vol II (WO 100/357) on pdf file page 226 of 357 (actual Roll page 217) entitled, “Pay Office Staff Imp.Yeo.”
His is the only entry on the page and reads:
Regt.No. 15730; Rank: Sgt.; Name: Robertson J.A.S.; Clasps: South Africa 1901 &1902;
Any other Corps in which served in South Africa: 78th Coy Imp. Yeo. Regt. No.15730;
Remarks: Embarked for S. Africa with 78th Coy 14 April 1900 serving in that Country continuously until discharged in S.A. at own request 8 Mar 1902.
Unlike some former soldiers entries, no address is given in SA, perhaps one appears on his I.Y. discharge document in WO 128.
The QSA Medal Roll for the 19th to 22nd battalions I.Y. is in piece number WO 100/128 but have had problems downloading it so have reported the fault to the NA. It will be worth looking at his entry in the actual QSA Roll as like his entry in the KSA Roll online records don’t show all the details.