I wonder if the heat from the car added an extra variable to the experiment, interfering with any other results. I'd like to see how that same experiment would work if the plants were left in a moderate temperature. Maybe the next time I'm cleaning out my crypts, I'll so a similar experiment. I'd want to put them in a box and try them indoors (cooler temps) as well as outdoors in the shade (warmer temps, but not hot). Then check them once a day to see when each began to show signs of degrading.
I remember reading somewhere long ago the reasoning for shipping plants with no extra water, newspapers, etc. Just put damp plants in the baggie, blow them up with air, and seal them. I want to say it had something to do oxygen, but I can't remember for sure. I know when people shipped plants to me, those in water or wet paper towels or newspaper arrived in poorer condition than those packed damp with nothing else. It's been so many years, I don't know if I could find that source anymore. It would probably be better to just test it out again. Just not with the heat from the inside of a car.