I have been thinking about this, if Izuna gave his eyes to Madara, why didn't he then take Madara's previous eyes, and both end with EMS?
Same for Itachi and Sasuke?
OK dude 2(ms)+2(ms)=2(ems)
The way i understand it is, 2 eyes are embedded into another pair of eyes. Then that creates ems. Both pair of eyes are "deleted" to create a new, powerful eyes that can never go blind and can upgrade to Rinnegan.
If that were the case then the both of them would have 1 ems
Madara was blind when he took his eyes