A pivot report compares two dimensions, such as Assignment group and State. It helps a manager see where a total comes from. A trend report groups records into time periods. An opened-date trend describes record creation over time; it doesn't reconstruct what the backlog was on each historical date.
Performance Analytics collects indicator scores on a schedule. Those stored scores support historical trends for measures such as daily open backlog. A current-state report only sees the fields and records available now. Indicators use an indicator source, a collection schedule, and breakdowns when you need segments. Keep the collection grain consistent. If a collection missed a day, show that gap rather than assuming the current count was also the count on the missing date.