Average Age Report "broken" for my Team

[Ron Sethman]

Good day, the issue I am encountering is one where the problem is the report working as intended and my team not following protocol, but unfortunately I still need a working solution. 

Further Detail:

Average age report takes the creation date versus the resolution date. The resolution date only fills in if the ticket moves through the entire flowchart; however, my team did not always move things through the whole flow and sometimes (oftentimes) would skip from "in backlog" to "Done" or another status. This has caused a large number of tickets to show as unresolved despite having either a closed or done status. Meaning that our Average Age report has tickets throwing out year+ dates and messing up our metrics. 

The question I need resolved is; is there a way I can edit this report so that it shows the correct data? My team does not have the time to re-open every ticket and manually put them through the workflow to correct the resolve status. Is there any way I can edit what field it is looking for, or another report that can show the average time from Creation to complete (either closed or done). 

Thank you!