docs(config): duplicate names are caught by the loader, not the hook

docs/derived-variables.md

@@ -78,7 +78,7 @@ Derived columns themselves are an EDIT screen feature: the VIEW screen and the d
 
 A configuration error - a bad name, an invalid type or length, a name collision, or a reference to a derived variable that is not defined earlier - stops the EDIT screen with a message naming the variable. A syntax error or an unknown column in the expression itself is caught when the view is compiled, and stops the screen with a message naming the table.
 
-Most of these rules are also applied when a row is submitted for approval, through a post edit hook on `MPE_DERIVED`. A bad name, type, length, format or expression - or a duplicate name, or a reference to a variable that is not defined earlier - is rejected at submit time, while the error can still be corrected, rather than breaking the EDIT screen afterwards. The collision between `VAR_NM` and a physical column of the target table is only checked at read time, as the hook does not have the target library assigned.
+Most of these rules are also applied when a row is submitted for approval, through a post edit hook on `MPE_DERIVED`. A bad name, type, length, format or expression - or a reference to a variable that is not defined earlier - is rejected at submit time, while the error can still be corrected, rather than breaking the EDIT screen afterwards. The collision between `VAR_NM` and a physical column of the target table is only checked at read time, as the hook does not have the target library assigned.
 
 The simple rules are also configured as validation rules on the table itself, so they show up in the grid before submission: `VAR_TYPE` is a dropdown of `C` and `N`, `VAR_ORDER` and `VAR_LEN` carry minimum and maximum values, and `VAR_NM`, `VAR_FMT` and `VAR_LOGIC` are pattern checked. Validation rules are evaluated in the browser, so the post edit hook remains the authoritative check.