dovecot - Sep 2019 - Namespace overlap

Given an existing default namespace:

namespace inbox {
   type = private
   separator = /
   prefix    location = sdbox:/var/mail/%d/%n/sdbox
   inbox = yes
   hidden = no
   list = yes
   subscriptions = yes
}

And mailboxes like:
INBOX
INBOX/Archives
INBOX/Archives/2018

if I then define a new namespace:

namespace archives {
   type = private
   separator = /
   prefix = Archives/
   location = mdbox:/var/mail/%d/%n/Archives/mdbox
   subscriptions = no
   list = children
}

What will happen to the previous existing mailboxes & mails? Will they 
simply be "masked" by the new namespace and remain pending other 
operations? Or would they be moved/deleted?

If they remain - is it possible to refer to the old mailboxes via either 
IMAP or doveadm?

-- 
Daniel