I know that the documentation to older versions of the Unity docs are available... somewhere online. But I can't find where. If I needed documentation for 4.6.2, at this point I would have to download 4.6.2, and read the bundled information. Which is a bit overkill. I keep running into situations on the forums where people ask questions about why things are not working, and I can't really answer without looking up the old doc versions. I think it would be really great if the documentation team implemented something akin to what you get on MSDN - a little dropdown on the top of the docs page where you can select what version of Unity you want to read the docs for. It shouldn't be too much work - you already have the documents around, and I'm sure that I've gotten accross them somewhere on the unity3d.com domains already, so you just need a little link. Pretty please?
I know we need a dropdown... it's on our list. (Which is enormous :-(). Look at: http://docs.unity3d.com/462/Documentation/Manual/index.html So, just add the version number and the string "Documentation". (Oh, and once upon a time we had a dropdown in the documentation home page. Which provided a link to a version page... But this stuff all broke.)
for anyone arriving through google it's now partially covered in here: https://docs.unity3d.com/Manual/ManualVersions.html although anything below Unity Version 5.2 returns 404