Move older messages to Old folder after a bunch of changes (sql + other stuff)

I'm starting to get things better done now. Moved to all virtual users over IMAP. Using a SQL database for users/passwords. Setting up folders working properly with neomutt.

Right now, that leaves me with just new mail in the INBOX, and other folders. I have a bunch of old mail in each users Maildirs in their real home folders. Right now, I'd like to move all the old mail into a folder (doesn't really matter what it's called).

Right now is actually a perfect time to do this by good luck in timing.

How should I go about creating a new folder for those messages and then adding the old mail from system user home Maildir folders to the virtual users folders I'm using?

Thanks for any help, Chris Bennett