With the first retina MacBook Pro, they split the displays between Samsung and LG, and the LG displays had some pretty nasty image retention issues, I had my display swapped due to them.
After I returned the 2nd laptop, I started opening the laptop in store to check for the issue and went through 4 more additional laptops before I got the Samsung display.
A couple of months later, in their repair catalog, Apple apparently created a new part number consisting only of Samsung displays and started replacing with a Samsung screen for all repairs.