We do update the online documentation for each release of the engine; however, that doesn’t necessarily mean every single change and new feature will be included in those updates.
In an ideal world, the answer is yes. Our goal is to provide you guys with quality, accurate, and complete (covering all features) documentation. The reality is that the number of engineers working on the engine at any given time is something like 20 times the number of people on our team writing documentation for the engine. We do our best to keep up with the changes in the engine, but we also push out changes to the engine to you guys at a blinding pace and generally as soon as they are in the engine. The result is that the updates to the documentation often lag behind the changes.
The life of a tech writer (aka documentalist, documentor, and lots of other awesome names) can be painful at times. We appreciate you guys in the community pointing out the areas where things are inaccurate or even just not clear or complete. We make notes of all of it and put it into the schedule to be worked on.