User blog comment:Tanavar/Is it just me?/@comment-957629-20130403160745

Isshin must have known about it somehow!! His own zanpakuto does Getsuga Tensho like Zangetsu so he must have known about The Final Getsuga Tensho somehow!! It does not say he learnt or achieved it but attempted to learn it since he knew about it!! If he knew about it then he must have at least tried to learn it!! There is no other reason for another Shinigami having so much information regarding another's zanpakuto before that user themselves knows about it!!