I've been calling good results from a single prompt "single-shot." Is this not right?

This is one-shot.

if you had one-shot

or one opportunity

It means there is zero training involved in getting from voice sample to voice duplicate. There used to be models that take a voice sample, run 5 or 10 training iterations (which of course takes 10 mins, or a few hours if you have hardware as shitty as mine), and only then duplicate the voice.

This you give the voice sample as part of the input, and immediately it tries to duplicate the voice.