ets no longer using SSN matching on student school code

How are other universities setting up their search match criteria?  We use to match on 4 digits of first, 5 digits of last, ssn and birthdate.   With ETS no longer supplying SSN, we need to map on a new field to limit the selections.  ETS has indicated that we can identify the student by their atp_cd (school code), but in file parser the field atp_cd is only available by organization not by student.  What are other universities doing?