Fast formula to check new hire/rehire for pending worker

We have to write a Fast formula which would check if an employee is hired for the first time.

The employees are hired through ORC, and always a pending worker first, so the action code would always be for pending worker so action code would not be useful.

The logic could be:

Check if: employee existed in the system before

If no, the Eligible = Y

If yes,

then check months between termination date and new projected date

If greater than 6, then Eligible = 6 

Need assistance to understand, how to include the first part in a fast formula (checking employee's prior record in the system)