Science is typically never complete nor fully certain. Science is more of a process, than a destination, particularly when it comes to incredibly complex biological organisms. There's almost something new to learn.

I posted that link to that WHO report in the original Ebola thread and it seems pretty clear that the intent of that passage is to say that there was someone with a confirmed case (although they don't define whether it was laboratory confirmed or just clinically confirmed) with an incubation period greater than 21 days. Also the way they broke down the percentages as 95 and 98%, it seems like it could be a probabilistic breakdown rather than an actual count, which means the 21-42 day group may not have literally been 3 out of 100 cases. Based on a probabilistic distribution, a single extreme outlier could span that 95-98% group (and the other couple percent left over are just missing data).

That said, I have not been able to find any clarifications or verification about that WHO report since I first posted that link, so I'm unsure how much confidence to put into that statement that there were some people with incubation periods beyond 21 days. Just as there is tremendous undercounting going on, I'm sure there are plenty of cases where just the wrong information is recorded, and that could easily turn out to be the explanation once the smoke clears.

But back to a point I just made above--our experience with Ebola in the First World has turned out much differently than most people--including myself--feared, based on what it does in African populations. The track record so far indicates a disease which is serious but which the human immune system can beat even without any proven treatments, and indicates a virus which does not rampage through the populace like the Norovirus on a cruise ship.

Regarding quarantines/isolation policies, the fact is that these policies are a combination of science and other political factors, so it is not surprising that different people in charge (like Gov Cuomo or Christie) come up with different policies. Now that some states have implemented their own quarantine policies, there is a big push to harmonize them but of course there is pushback on many sides. If policy were based solely on good science, in my opinion, we would probably follow something like the MSF guidelines that Dr Spencer was following in NYC when he became symptomatic. Policies based more on theoretical risks and trying to appease the public end up looking like New Jersey's original policy of mandatory 21 day quarantine, no matter what.