Why are UA´s 777-300ERs designated as -322ERs and 787 and 737 designated as with the -24 customer code?
If they are, it is because someone made it up.
Boeing no longer uses the codes. But certain types will want to attach they airlines code anyway. Nothing stops some one internally from calling it a 322ER if they want to.
On the flip side, maybe someone could call the 787-924. That is also imaginary but it wont stop people from doing it they want. Doesn’t make any of it real.
You will never see anything public facing using these imaginary codes.
In the past the app may have noted the difference between a 777-222 or a 777-224 but at this point even the REAL codes any no longer displayed (just -200) and certainly not pretend ones.
FWIW, I imagine the old sUA 772 would be the last planes ever delivered with a -22 code from Boeing. CO order aircraft would have continued with the 24 code even after the merger till these were discontinued