Which image should replace the question mark (?) if the following series were…

This is a figure-matrix series with six fixed cells in every box: one top-left corner, two middle cells, and three bottom cells. A rotating corner-pair occupies the top-left and bottom-left corners at a time, swapping corners from one box to the next; every two boxes, one corner member is promoted into a single reserve cell, the other corner member retires from the series for good, and a genuinely new symbol, never seen anywhere before in the series, whether letter or digit, joins the promoted member to complete the pair. Meanwhile a separate fixed trio of symbols (one letter and two digits) continuously rotates through the three non-corner cells that the reserve letter is not currently occupying, and never touches the corners.

Tracking the corner pool and the reserve cell across the four given boxes:

1. Boxes 1-2 form one corner-pair cycle: K and X occupy the top-left/bottom-left corners and swap between them, while W sits in the reserve cell (bottom-middle in box 1, bottom-right in box 2).

2. At the end of box 2, K is in the bottom-left cell, so K retires from the series completely; X is in the top-left cell, so X becomes the next reserve letter; and W, the outgoing reserve letter, is promoted into the corners together with the brand-new letter T. This is exactly what boxes 3-4 show.

3. Boxes 3-4 form the next corner-pair cycle: W and T occupy the corners and swap between them, while X sits in the reserve cell (bottom-middle in box 3, bottom-right in box 4).

4. At the end of box 4, T is in the top-left cell, so T becomes the next reserve letter; W is in the bottom-left cell, so W now retires from the series completely, the same way K did earlier; and X, the outgoing reserve letter, is promoted into the corners. The rule only requires the incoming corner symbol to be entirely unprecedented in the series (as T was, two boxes earlier) - it is not restricted to being a letter. Every letter and digit used so far (K, X, W, T, L, 8, 2) is already accounted for elsewhere, so the corner slot must be filled by a symbol that has never appeared before; the digit 9 satisfies exactly that requirement.

5. The middle/right-hand trio keeps rotating on schedule: L sits in the middle cell for odd-numbered boxes and the middle-right cell for even-numbered boxes, so box 5 (odd) places it back in the middle cell; the two digits swap which of the middle-right/bottom-right cells they occupy every time a new corner-pair cycle begins - box 1 had middle-right = 8 and bottom-right = 2, box 3 flipped this to middle-right = 2 and bottom-right = 8, so box 5 flips back to middle-right = 8 and bottom-right = 2.

6. Putting it together, box 5 must show: top-left = X, bottom-left = 9, bottom-middle = T, middle = L, middle-right = 8, bottom-right = 2.

Checking each figure against these rules: two of the given figures place a digit in a corner cell, which never happens in any of the four given boxes; one figure never introduces the required new symbol at all, simply reusing letters already seen; and one figure brings back a letter that must have permanently retired at this transition. Only the figure with X in the top-left corner, the new digit 9 in the bottom-left corner, T in the bottom-middle cell, and L, 8, 2 continuing their established rotation satisfies every rule simultaneously.

Correct layout: top-left = X, bottom-left = 9, bottom-middle = T, middle = L, middle-right = 8, bottom-right = 2.