The surname must have an entry for the search to work.
Inappropriate entries may result in incorrect or no data being returned.
One useful strategy for finding what you require is to enter some appropriate criteria, view what appears, and, if too many results are shown, use 'Change search values' and alter the criteria to narrow the results and rerun the query.
Field notes:
Surname part - any string of 2 to 12 letters or spaces that are in any place within the surname fields, not case specific (see below for wildcards- useful if used when unsure of spellings of names)
Wildcards - these are symbols that denote an unknown part of a string; % indicates 0, 1 or more characters and _ (underscore) a single character in a search. For example, using 'sm_th' will find smith and smyth. Also, remember that the chosen pattern of letters and wildcards can be anywhere in the field, eg: in surname, ST%L (or lower case) will find STarLing, conSTabLe, STeeLe, paSTaL, etc. Wildcards cannot be used in number or date fields.