Board Thread:Theories and Speculation/@comment-30787246-20161219014910/@comment-27924662-20161219051009

all this makes sense but in the filler they showed Ashura too using all the wood tech (particularly the 1000 handed Buddha). So my guess is that hashirama eventually recreated the tech on his own while he mastered the wood style. (just like tobirama creating edo tensei, shadow clone, and other such jutsu).