Full list of non-zero Kazhdan-Lusztig-Vogan polynomials:

 0:  0: 1

 1:  1: 1

 2:  2: 1

 3:  3: 1

 4:  0: 1
     1: 1
     4: 1

 5:  0: 1
     5: 1

 6:  1: 1
     6: 1

 7:  2: 1
     7: 1

 8:  3: 1
     8: 1

 9:  0: 1
     1: 1
     4: 1
     5: 1
     6: 1
     9: 1

10:  5: 1
     7: 1
    10: 1

11:  6: 1
     8: 1
    11: 1

12:  0: 1
     1: 1
     4: 1
     5: 1
    12: 1

13:  0: 1
     1: 1
     4: 1
     6: 1
    13: 1

14:  2: 1
     7: 1
    14: 1

15:  3: 1
     8: 1
    15: 1

16:  0: 1
     1: 1
     4: 1
     5: 1
     6: 1
     9: 1
    12: 1
    13: 1
    16: 1

17:  5: 1
     7: 1
    10: 1
    12: 1
    14: 1
    17: 1

18:  6: 1
     8: 1
    11: 1
    13: 1
    15: 1
    18: 1

19:  5: 1
     6: 1
     7: 1
     8: 1
     9: 1
    10: 1
    11: 1
    19: 1

20:  0: q
     5: q
    12: 1
    13: 1
    14: 1
    16: 1
    17: 1
    20: 1

21:  1: q
     6: q
    12: 1
    13: 1
    15: 1
    16: 1
    18: 1
    21: 1

22:  5: 1
     6: 1
     7: 1
     8: 1
     9: 1
    10: 1
    11: 1
    12: 1
    13: 1
    14: 1
    15: 1
    16: 1
    17: 1
    18: 1
    19: 1
    22: 1

23:  2: q
     3: q
     7: q
     8: q
    19: 1
    23: 1

24: 12: 1
    13: 1
    14: 1
    15: 1
    16: 1
    17: 1
    18: 1
    20: 1
    21: 1
    22: 1
    24: 1

25:  2: q
     3: q
     7: q
     8: q
    14: q
    15: q
    19: 1
    22: 1
    23: 1
    25: 1

26:  2: q^2
     3: q^2
    23: 1
    26: 1

135 nonzero polynomials, and 81 zero polynomials,
 at 216 Bruhat-comparable pairs.