The variations mentioned were two huge Reed avocados (instead of Haas or Pinkerton), red onion, extra lime juice, and two-ish tablespoons of avocado oil. I've read that extra lime juice can help prevent browning. Some recommend putting a layer of oil or water on the leftover guac. In fact, I've read in several places that Reed avocados shouldn't be used for guacamole because they contain too much water, which is crap, btw.
Could the excess water in the avocados be helping hold off oxidation? I've put oil onto cut avocados and that slows things down for a day or so (with the pit in), and I did add avocado oil to the mix, but THREE FREAKING DAYS? Wow. Depending on the age of the avocados, I've had the stuff go brown in an hour. I'm not complaining here, but I'd love to duplicate whatever it was that I did and save the waste in future snacks/meals.
Everyone has an idea of how to accomplish this feat. Well, except me. I didn't leave in the pit. I didn't use a layer of water or vinegar. I didn't even TRY to keep it green. I made it, we ate it, Wonder Woman put it into a glass storage container with a plastic lid, and it went into the fridge. Every day since, ta-da, miraculous deliciousness. Not even once have we skimmed brownness off of the top. Weird.
If anyone has some science to explain this, (I'm looking at you, Doc Gus), I'm ready to listen. Meanwhile, I'm going to try and duplicate the results with different avocado varieties and switching up the other ingredients. I'm betting that the combination of the water in the avocado, the avocado oil, and the lime juice are working in cahoots, but that's just a notion at the moment. I'll report any explanations/findings here. The truth is in there.