Welcome to the Forums.
I think your desired goal can benefit from the ideas on this excellent link:
(kettan, this shows up on my browser as a highly visited site. Thank you again for it.)
If this all works well with your setup, you can add a Key column of all 1s to your data worksheet,
and then the make a new sheet of the same Key column and then a column of all the possible dates.
This creates the combination of all possible dates, but it can be filtered using:
AND [Date]<=[Discharge Date]
From here, I returned the Start IDs and The DC IDs:
IF [Date]=[Start Date] THEN [ID] END
IF [Date]=[Discharge Date] THEN [ID] END
You can also CountD these:
COUNTD(IF [Date]=[Start Date] THEN [ID] END)
Then you do a Running Total on the Delta:
[CountStart] - [CountDCs]
This Delta calculation should be amenable for graphing.
There are some nulls, I wasn't sure you needed them padded to zeros.
Thank you so much. Your response was incredibly enlightening.