Hi Steve,
I thinks that's an abbreviation for supernumerary, ie he ceased to be a regular member of KH on that date that has been lost on the page. I guess the supernumerary men must have stayed with the unit in some capacity otherwise they would have been discharged?
The QSA roll (WO100/256p26) show CC and OFS clasps, record he was discharged 24 Apr 1901 and that the QSA was issued to him 18 Jul 1902.
His KSA roll entry (WO100/256p96) records his entitlement to the SA01 clasp and gives an address of 73 West Dock Avenue, Hull.
There are attestation papers for KH in WO126/83-88 which may give you a little more information.
Regards
David