After the board problems in the movie were addressed Bill was still suffering resets but they weren't happening until much later in the game. Ultimately the problem turned out to be bugs and quirks in the
Missile Command code.
There was a
thread on the Twin Galaxies forums a couple of years ago where Bill explained the secret to marathoning the game (Bill is 'Sk8god' on the TG forums) and the discussion later evolved into some code analysis. It comes down to never having more than 255 cities in storage. (Actually, as it turns out it's more complicated than that; you can't have 256 cities +/- 3 at the completion of a board.)
Here's where it gets complicated. On the game's default (marathon) settings you are awarded a bonus city every 10,000 points. At 810,000 points you are awarded 147 bonus cities unless you already have too many cities in storage, in which case you will be awarded none. Then you are awarded no more bonus cities at all between 810,000 points and the 1,000,000 point rollover. When you reach the 0x ("zero times") boards, which are board numbers 255 and 256, every action that results in points awarded is multiplied by 256. This means you get an unbelievable amount of points on these boards. The problem with that, of course, is that you still get a bonus city every 10,000 points if you are not in the range between 810,000 and 1,000,000, so you again have to be mindful of your city count before reaching the 0x boards. Score rollovers happen at 1,000,000, so the next time your score reaches 810,000 again you will again be awarded 147 bonus cities unless you already have too many in which case you will get none, so you again need to run down your city count before hitting 810,000. As your marathon game progresses you have to worry about these two events eventually converging (810,000 and the 0x boards), so you need to keep accurate track of how many bonus cities you have at any given time, and know when to let the game kill off the majority of them before you can proceed past these various checkpoints. A good strategy is to let the game kill off your extra cities as you approach 800,000 until a wave starts where you see fewer than six cities on the screen. At that point you know exactly how many cities you have. Once you pass 810,000 you will be awarded another 147 that will help carry you until the million point rollover and you start earning bonus cities every 10,000 points again. The key is not to let the city count reach 256 +/- 3.
I hope I got all of the details correct and I think I did. Bill's problem now is not that the hardware is unreliable or that the game is still randomly resetting. He has to get more disciplined about keeping accurate track of his cities and taking breaks at the right times.