I don't buy it. They assign value when then invest (which of course is a very rough estimate). What's so hard about assigning a value a few months or years do

I don't buy it. They assign value when then invest (which of course is a very rough estimate). What's so hard about assigning a value a few months or years down they road when they presumably have a lot more info about the biz than they did on day 0 (the initial investment/mark).