Ligon II was another Capella IV. It had a substance the Federation needed, so the law was bent just enough not to tweak the PD's nose, while ensuring that the substance was obtained. (Ligon II was from the episode "Code of Honor".)
I think the problem we have when valuating the PD in the 23rd or 24th century is that we are viewing its interpretation through the perspective of four captains and their crews. The shows rarely explored the Federation or Starfleet beyond the narrow confines of these three captains. We know from the mission orders sent to a handful of ships in 2364 that starship captains had the discretion to initiate first contract proceedings with a pre-warp civilization. And, we know from the testimony of Q Junior, that Captain James Kirk did receive some kind of recognition for rescuing two civilizations from destruction, while at the same time violating the PD.