Most of the earlier hid kits were rated at 35 watts. The 55w kits were false as they were rating them at their stepped current at startup. As 55w models became more popular, the bulbs improved as well by improving the tungsten electrode and gas contained in it to handle 55w or more of current.
Since it is the gas that creates the light, it requires only a certain amount of current after the arc to maintain its state (where the molecules release photons which is what creates light, or something like that), which can be 35 watts minimum up to 55w or more.
So, early made bulbs that werent rated to 55 watts, would usually just burn out. A too high rated bulb that required a minimum of 55 watts and running at 35 would also burn out early as there would be insufficient current to maintain the gas molecules at its reactive state.
Hows that for a good guess.