Board Thread:Naruto Discussions/@comment-2245550-20160501143136/@comment-734582-20160503105339

X29 wrote: You said they were aware of almost everything he's done, which leaves space for Madara taking Hashirama's flesh. If he and Orochimaru were aware that combining Uchiha and Senju DNA would bring forth the Rinnegan, they'd have already had it by now. They actually were aware of that. As Kabuto says in ch. 560 they believed the Sharingan could become Rinnegan. They were unaware of the transmigration requirement however, which is why their attempts failed. And the conversation indicates they knew Madara could've survived death though Izanagi and gained Hashirama's cells through their fight.

So again, the only thing missing was the transmigration requirement, because though they did have Hashirama's cells they never had Madara's DNA.