dovecot - Oct 2020 - 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