[Dovecot] Restoring older messages to new server?

I had Dovcot 1.x setup, all was working well (till...)

Server got stuffed up and same Dovecot 1.x was rebuilt, put back in service, all's working well.

I have recovered data from Maildirs messages from the old server,

As some of the inboxes now have new messages, what is correct way to copy older messages from old server to new server ? (There are no duplicates, simply old messages from past server, data is physically on new server)

Thanks for pointers, Voytek

Swyped on my Motrix with K-9 Mail. Please excuse my brevity.