I'm not if I completely understand the point below and would appreciate some elaboration.
"This Package-on-Package construction gives Apple the flexibility to source the RAM from any manufacturer they want—they're not locked into Samsung."
I understand that PoP construction makes it technically feasible for to combine logic and memory chips from different makers. However, does this ever really happen with Samsung? I feel it would be unlikely that the logic maker (Samsung) would allow Apple to use anyone else's memory, given that Samsung makes both logic and memory. Can anyone share their experience?