Spoiler - 2008 Exam IPS Time Horizon Question

Why is CFAI so damn inconsistent when it comes to number of time horizons? I’ve seen some cases where they are take a broader stance, like in Question #1 from the 2008 exam and in other times they split the time horizon up whenever there is a somewhat meaningful change. For the time horizon constraint on the 2008 exam I figured that it was a long-term / multi-stage horizon with 3 time horisons: 10 years until the trust distribution 20 years after that until retirement 30 years >> retirement With a possible additional time horizon if the kids end up going to college, but don’t get the free tuition. This is in line with the CFAI explanation except that they don’t include the middle time horizon. I thought that it should be included because: a. Their liquidity constraint and required returns are considerable for the first 10 years until the 2nd trust distribution takes place b. Their ability to take risk increases once they receive the $750k distribution (which represents a substantial increase in their asset base). Any thoughts? How much do you think CFAI would have taken away for including the middle time horizon?