http://mobilesemi.blogspot.ca/2014/09/apples-64-bit-processo...
By Oct. 2012, Samsung had licensed the A53 and A57 core designs: http://www.techhive.com/article/2013298/arm-introduces-64bit.... . They didn't have 'many details'; they had the design itself.
ARM designs are like a GIT repository, and the AXX continued having revisions and changes through 2013. Running with it early and you are bound to either go on a detour or end up with a noncompetitive variant.