Accurate Headcount Reporting in OTBI even after department change

My goal is to accurately reflect the headcount by department, ensuring that the count includes only active employees, even if they have changed departments.

Currently, when summing the headcount by department, the report shows counts such as '4' and '1' for the same employee, which leads to double counting. I need the report to show '1' in both places, reflecting the correct headcount for each department.

Additionally, the report should be able to display past dated headcount accurately when a termination quarter is selected. This is crucial for calculating attrition rates function-wise.

Here are the specific requirements: