Desired end result: A pivot table that counts employees onboard by month.

The spreadsheet that I have is massive. It has over 10,000 employees and all the charge objects they could charge to in a day. So 1 employee will have multiple rows. What formula can I use to only count an employee once for each month (if they were onboard)?

Simplified version (the report has several other columns):
Col A Col B Col C Col D
Name Month Charge Object # hrs

Thank you in advance. You Excel Angels always bail me out on by work projects.