I will do the first part &mdash; though it essentially does what `$authority->post->post_excerpt` does (except `0` would probably evaluate as false).

`get_the_excerpt()`, however, retrieves the first-post-in-the-loop's excerpt because it relies on global `$post` objects and doesn't support the passing of an ID.  Looks like there is a [ticket open](http://core.trac.wordpress.org/ticket/12976) for this that just hasn't progressed in ages.