By design, most of the filter fields only search student records and do not include prospects in the results.
To find prospects, use the Inquiry Forms criteria at the bottom of the filter options.
Example
For example, to filter on prospect programs, use the "Submitted Program Interests Include/Exclude" filters in the Forms section vs. the Student Information section "Programs Include/Exclude" filters that only searches for student person type records.
By design, student information program filters will only return students that fulfill the program criteria based on their primary program imported from the SIS on the Transcript data feed. To learn more about Student Filter options, click here.