This tissue is referred to "UCA Conformance Test Procedures for Server Devices with IEC 61850-8-1 Edition 2 interface Revision 1.0" + "TPCL version 1.2.1".
1) I think that "PIXIT Ct18" should be mentioned in "sCtl10", "sCtl15", "sCtl16", "sCtl18", "sCtl21", as it is mentioned in "sCtl7", "sCtl17" and "sCtl19" test cases.
2) Additionally, in "sCtl16 test d.1)" should indicate "Client sends SelectWithValue request, on response+ sends Operate request" as "sCtl15 test d)" does.
3) On the other hand, why in SBOes internal validation can be performed in SelectWithValue or Operate (PIXIT Ct18) and in SBOns it has to be done in Select? For example, see "sCtl15" or "sCtl16".