Chosen Solution
Just make sure you removed all of the screws. Here’s a good reference: MacBook Pro 15" Retina Display Late 2013 Lower Case Replacement. I’ve encountered a few covers which were a bit harder to take off just take your time here and ease it out one side at a time. Sometimes it’s the screw seal that has oozed out a bit that acts like glue. Update (04/28/2016) Apple has two versions of bottom cover & chassis for the 15" models. One has Black plastic slots and the other has White colored pads Black slotsWhite pads (just one side visible here) Personally, I haven’t encountered any issues with either.
