Can incidents be manually archived or set to dormant?

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As well as new incidents, we imported a lot of incidents from our previous CRM which were uploaded 3 years ago.

In an attempt to improve the system and report performance we want to look into setting incidents to dormant, then archived, then purged which will be fine for the current incidents and i have read the relevant documentation on how to do this.

The problem with the imported cases is that the date created and date closed dates are (as far as the system is concerned) only 3 years ago. I can report on when these cases were originally closed as we have a custom field for historical date closed but i want to know if i can manually archive them or set them to dormant?