Yes! This was the solution! Thank you so much for your help, Karen I removed the date range and the rest of the patients populated the list! It was looking for exam dates, which skewed the results.
If you need them separated into a date range, you can try the other date range categories to narrow it down as opposed to using the "Last Exam" category.. There is also a "Last Invoice" and "Last Appointment" date range categories.. The "Last Exam" is going to only pull invoices with billing codes that have a full exam designation.. This is in contrast to the "Last Invoice" category which will pull all patients with an invoice in a certain date range regardless of whether or not an exam code is on the invoice, and the "Last Appointment" category which should ignore invoices altogether and pull patients who have been on the schedule during the date range selected.