That's good to know. It's 35 years too late, though. I wrote the Donkey Kong cartridge for the Atari 400/800 computers, and wish I'd had this kind of information when I was writing the barrel code.
I think I just added more vanilla barrels, more wild barrels and more X-velocity jinks to increase the difficulty. I was totally guessing just based on a few weeks of playing the game intensively.
There is a really interesting documentary about world record arcade gamers called "The King of Kong" [0] that follows people who try to get top scores in Donkey Kong and other arcade games. Its enjoyable and interesting, I highly recommend it.
I think this is very cool. However, I wish that it could be framed in a context of strategy at the game. For example, knowing that I can influence the behavior is only the first step for me to know how I can exploit it for profit.
The most common place to use barrel control is on the platform below Donkey Kong (where the upper hammer is). When you have the hammer, you want to force the barrels to come down the ladder closest to Donkey Kong, so you can hit more of them with the hammer. You can then continue to force the barrels down that first ladder as you make your way to and up the ladder at the end of that platform as efficiently as possible.
More advanced players will use barrel control to group 2 or 3 barrels together so they can jump over them for more points.
Check out The King of Kong: A Fistful of Quarters to learn more about Donkey Kong and classic arcade games in general.
I think I just added more vanilla barrels, more wild barrels and more X-velocity jinks to increase the difficulty. I was totally guessing just based on a few weeks of playing the game intensively.