Board Thread:Wiki/@comment-27441457-20160627051627/@comment-5774380-20160627130039

It could also be the opposite case. Whenever a spin-off is in production, the mangaka is called to give advices to the writers about the setting and elements of the story (not only in AoT's case but in pretty much any manga). Maybe he told the Before the Fall team about the Iron Bamboo and the Iceburst Stone and they applied them to their story before Isayama wrote the guidebook. So I don't think this has any effect on the current non-canonicity of Before the Fall, we need to find an unquestionable proof; preferably a character or an event from the spin-off affecting the main storyline somehow. Items are too diffuse.