count unique values in columns based on date values

I manage a call center with staff levels that fluctuate from 12 to 120 agents. I have a workbook that allows me to manage current and upcoming projects. I use the countunique function to give me a headcount based on names entered into a named range "enrollers3" Basic project information such as start / end date are in the rows above my named range.

I am trying to forecast headcount based on project start / end dates. Agents may be assigned to multiple projects simultaneously or be listed on a current project as well ones with future start dates.

I have several macros which allow me to sort projects based on criteria in the cell values above my named range. I want a summary sheet which in column a has date values and then in column b the unique headcount for that particular day. As projects are added / dates changed / staff deleted or assigned, I need to be able to reference my summary sheet and see how many unique heads will be in the call center on that day.

Much obliged for any assistance. I am beating my head against the wall with this one.