Do notifications occur when changing a blog entry to 'published'

We want to be able to 'publish' a blog entry with an 'unpublished' status (see attached screenshot)
-- we are hoping that notifications to subscribers won't be sent at that time .. is that true?

When we change the status of the blog entry to 'published' , will notifications to subscribers be sent out then?

and a final question along these lines. We have some blog posts that were created before we enabled notifications. Is it possible to trigger notifications for those older posts? (perhaps by unpublishing and republishing them ?)

Many thanks