Originally Posted by Rikudounaruto

I understand it from start that you wrote about current old Madara in manga, who has only spare sharingan in left eye.


It could explain where Obito got second sharingan, but maybe it was while Uchiha massacre.

Please read my prediction above - 604 - Cursed World,
My explanation is that Madara died as in process of his body merge with Obito body, making Obito as grown up man. Obito got Madara knowledge, talent and expierience. Thanks to madara talent Obito deveopment was accelerated so he learn faster how to use sharigan, Mangenkyou sharingan.