When I was in high school (in the 80s), me and friends ran a second-run movie theater. The oldest among us were teens, and the real owner hadn’t stepped foot in the place in years.
We lived off of popcorn, but it had to be fresh. First, we would add an obscene amount of Flavacol to the oil and kernels. Then we would load the popper and place a bucket under the popper to catch the popcorn. This was the only way to truly enjoy popcorn.
Our popcorn popper broke one day, and we called one of the big movie places nearby, and they agreed to give us some to hold us over. The guy brought me to a room that contained large black garbage bags filled with popcorn. It was disgusting. The guy told me that this is how it was done. They would pop the corn once or twice per week, fill large garbage bags, then bring it down to the “poppers”, which actually didn’t work. They depended on the heat lamps to warm it up (for the smell and the impression of being fresh).
I’m not sure if that’s standard practice, but I haven’t consumed popcorn in a movie theater since.