With the new "Multi-person" forms, we can "Link" the submission to an existing person, but we cannot find the way to "add" the submission as a new person when reviewing the submissions.
We would also find this much more useful with these improvements:
Thanks for the post!
When it comes to adding a person from a form submission this should happen automatically if the form is set to add people to the database and you've approved the form submission. It might be best to email us with specifics about the forms this isn't working on if you're having issues though and I'll look into this.
Regarding the other improvements, the custom redirect URL and message is something we're wanting to look into in the future. I'll add a feature request to allow customising the 'Add Another Person' button though.
Hope this helps,