As others have said, I think is just accelerating the 20 A320s that were scheduled to be retired this year, plus maybe one additional frame. I am aware of the one frame retired in January but Kirby mentioned 21 frames so may be another A320. If you look at which A320s have received NEXT, almost all of them are 2001 builds or later. Gives you an idea of where the pre-2000 builds are headed, mostly to be retired and will not receive NEXT. The A320 is the ugly stepchild in the current fleet. Small F Class, the FAs didn't want another row of F because it meant 1 FA serving 16 upfront, and seats 150, the maximum allowed for three FAs. Compare it to the 738 and 737 MAX 8s that have four FAs, with two upfront. And I haven't even gotten to fuel burn which the 738 does better than the A320. The one fleet that remains a mystery is the 73G fleet. Just 40 of them and they are heavily used for short runway operations. Wonder if UA can just park those and use the 738 SFP as a substitute, knowing that there will be seats needed to be blocked for some airports or UA can take delivery of the A321neos with one ACT tank. That would make SNA-EWR on a non-73G a reality.