Filtering in Validation

[WLMPilot]

I am creating a scheduling system for an EMS service. I have a single list
of employees (AA:AB) that I can use to create a LIST via validation.

AA:AA = Employee Name
AB:AB = Certification ie P=Paramedic, I=Intermediate, B=Basic, D = Driver

I want to filter based on certification in the validation option so that
only paramedics appear for the medic shifts, etc. Is there a way to filter
within the validation or do I have to create four separate lists?

Thanks,
Les