Quick glance through the battlemech quirk list shows a lot of revisions, some of which contradict recent books, like Second Succession War (battlemaster lost it's weak head armor).
On the one hand, a purist might say that one or the other is in error. On the other hand, quirks are highly variable so, there's no reason both sources can't be true. It's a conundrum. One that decides just how exciting it is to drive a locust (no torso twist and cramped cockpit with no arms, or just no arms?)
Please don't take this as criticism, but simply me having not yet gone through the book enough to properly gush about it.