I see some comments about 1 v 2 satellites. When CNN started drawing two boxes a few days ago, I assumed they had reads from two satellites. Now that they've released the single arc picture, it makes sense why. Even if the plane was in range of two Inmarsat satellites, it doesn't mean both recorded the ping registration.
Think of that ping like your cell phone. Even if you hit 3 towers, the only one that will record your checkin is the one that holds your registration at that moment. It's very possible that, like your cell phone, the SATCOM decides which sat is the right sat to register with, and it will make that clear in it's ping. Then, the other one knows to disregard it.
Can't answer Q's right away since I'm driving.
I'm really curious as to why Inmarsat hasn't released the arcs for the other 5 pings. Couldn't hurt anything.