NMCLL is the name given to the last layer of corners when the stickers don't match. Common methods that use this include Roux, ZZ, Petrus, and CLL and EG for 2x2.
During a solve, it isn't initially required that the bottom layer of corners match. In Roux, for example, this gives four options for the second block. These pseudo blocks also have an effect on the last layer. More stickers from the F, B, and D layers can be mixed in. While any recognition can be used, the traditional ways are difficult to use with all non-matching corner types. A recognition method has been developed specifically to solve this problem and works equally well with matching and non-matching corners. All of the same algorithms can be used, though memorization of two patterns per algorithm is required. Because of this, current CLL users are reluctant to relearn recognition and most Roux users almost exclusively use matching or opposite blocks.