There is an issue in Custom Reports where fields are available for selection as data but are not available to be sorted in the output. Example is Name(Surname, Given) is available as a data field but not available for selection for sorting. You can only select either Given Name or Surname as sort fields.
Any data column should be available for sorting in the output.
So you want to sort by surname then? You can do that. In fact in RM8 if you choose to sort, Surname is the default and as a secondary sort, given name.
The Column date of Name - Surname, Given is the date in the column, not a specific format. You have to choose the part you wish to sort on.
