Someone has already mentioned the fact that Family Sims don't get their "Graduate 3 Children" want satisfied if they are not present when the third comes back from their final exam, but there is also a similar problem. Popularity Sims who achieve their 20 Best Friends Lifetime Want on another lot (for instance, at a party) do not get credit, either. A box comes up saying they've achieved it, but they don't get permanent plat or the Lifetime Want memory. Similarly, we can probably also assume that if a Sim calls another Sim and they become best friends and that gives the called Sim 20 Best Friends LTW, they won't get their Lifetime Want achieved either. The second one is particularly problematic because there is no way of knowing when it's happened.
I had someone try to reproduce the "Graduate 3 Children" bug, but they were able to do so. Is it consistently reproduceable? Are there any hacks that interfere with want check trees or otherwise in the related global trees? I don't want to blame it on hacks, but we've been unable to reproduce this--perhaps we could get better repro steps? I can have someone look into the 20 best friends thing, but no guarantees...
I've had a different problem with graduations that recently affected sims with the "Graduate 3 Children" bug. It's not the bug that's been referenced here, in fact, it doesn't really have to do with the LTW itself.
Essentially, when a sim graduates, his relatives all receive the graduation memory. Well, I've found that no matter how the sim graduated, if during adulthood the sim achieves another major accomplishment that would show up on relatives' memory panels, all the relatives will also get a "[X Sim] graduated Cum Laude" memory. This affects sims with the Graduate 3 Children LTW because this counts as a graduation. I've discovered this happening when a sim reaches the top of a career, that all of his relatives receive the memory that he graduated Cum Laude. I'm not certain but it's also possible that it happens when a sim gets married.
It doesn't actually change the graduation status of the sim (that is, if he graduated Summa Cum Laude it still shows as such on his diploma) but it does count as a graduation on every relative's memory panel. This can enable sims with the particular LTW to achieve it with only one or two actual graduations.
Just something to look into, although it is a bit less significant than most of the other bugs mentioned.