When an essay is asking to stay under a word count, they want basic, concise, clear statements. All of those apllications will need to be read and without a limit, people would write pages and pages. With a 500 count, you should be able to write what need to in 350-475. If it's 350, it should be very clear and concise. If you are up to 500, that's ok, but make sure you don't have a couple of "rambling" sentences or vague topics that need extra explaining. There isn't an "unwritten rule" about disregarding anything under 400 or 300, but as the word count becomes less, it need to be more and more precise. They will disregard 50-75 word though. Make sure it's not preachy or desperate...like "this is my last chance to do something with my life" or "I really need this." Give good qualities about yourself and what goals you are hoping to obtain (or whatever they are asking).