Above two are right of course. Nothing more to be said about this topic specifically.
But I'd like to say that this is a FANTASTIC example of how good design improves lives with almost no drawbacks. Shimano could *easily* have chosen to design a splined interface that's radially symmetrical and thus requires careful installation to align. And then if you screwed up the install, Shimano could blame you, the user, for not following their instructions or whatever.
Remember this next time a company tries to blame the user.