Demand Planner's overstock report identifies where your warehouse has more inventory than is required to meet demand. The report can be accessed via the left side menu.
Excess stock is a factor of the forecast to cover the lead time and days of stock specified for each variant. Items forecast to have excess units available after your planning period (the end of the lead time + days of stock) will be identified as overstock.
In the example above, the planning period ends on December 4th. It is forecasted that on that date there will be the number of overstocked units indicated here.
The date filters can be set to show historical metrics such as sales and revenue for a given time period. This date range will not affect the forecasted units that will be on hand after the planning period.