Pulling Incident Backlogs

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Hello,

    We are attempting to pull our incident backlog however we have a tricky question but perhaps someone here knows how we could pull this data.

We need to find out what our backlog looked like on 2/1/2016, 3/1/2016 and of course 4/1. We want to know, on the 1st of the month... how many open, unresolved tickets we had at that moment in time.

Can someone help? Perhaps there is a specific formula or filter that I could use on a basic ticket report.