One think to remember is that if a local culture has already learned about extraterrestrial life before the Federation arrives, then that portion of the prime directive doesn't apply any longer. Considering that the presence of a civilian Vulcan trader on Organia was not seen as out of the ordinary, Starfleet wasn't concerned about revealing themselves. I assume a similar sequence of events on before "A Private Little War".
That's right! I feel like Rok when he realised he could override his programing. No matter how "primitive" the culture, if they had knowledge of aliens and other worlds then it doesn't fall under the Prime Directive!
And that's the rub. Unless the Federation puts all its resources into picket ships and blockades around systems of pre-warp (or just skip that retcon, call it normally developing worlds), then what is to stop Harry Mudd or Ferengi or Cyrano Jones from waltzing in and telling all about the galaxy or the quadrant? Or selling them impulse engines, or warp drive for that matter?
PD is utterly unenforcable, except with respect to Starfleet personnel (with obvious exceptions.) Also it is ridiculous, and as a villain of ethical stature in early Bantam Trek novels put forth, "a policy of mass murder."
The other thing to keep in mind here is that B&C was credited to both Coon & GR. So you have the guy who came up with the prime directive (and the klingons, and pretty much everything else of enduring interest and value) being rewritten by the series creator, so there's no telling how the PD worked in earlier drafts. Could be they were both on the same page -- it's easy to see B&C as a reflection of their feelings about the network, censorship and the industry as a whole, and the show remains one of the more biting bits of satire in the whole run.