That makes sense!
I’ve been able to confirm that for a staged user (who hasn’t been activated), this works nicely. If I’d followed up on my original message by sending out invitations direct (ie, “Restricted to this email address”, then click the “send invitation email” button) to those email addresses, they can just click the invite link and create their account.
I can’t do this to an activated staged user: in that case, trying to invite them fails because that email address is already associated with a user account.
But since a staged user should not ever be able to be activated, that shouldn’t be a problem 
This was of course a “restrict to N uses” invite. I’m not sure if that makes a difference in terms of being able to use the invite - but given what we’ve already found, I suspect that this invite link would have worked fine if I hadn’t already activated the accounts.