The Performance report stores data for up to 6 months. Aside from "normal" data, it will include:
• Duplicate extensions:
A user configured as different extensions in the last 6 months (Ex. ext 1134, ext 1123) will show it on the list since it would have been accurate in the past call data.
• Deleted extensions:
Deleted users are retained on the report to retain accuracy, otherwise, you won't be able to get accurate info about past metrics. You should see the “i” sign next to the deleted user, company number, or queue.