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

0: 0: 1

1: 1: 1

2: 0: 1
   2: 1

3: 1: 1
   3: 1

4: 2: 1
   3: 1
   4: 1

9 nonzero polynomials, and 2 zero polynomials,
 at 11 Bruhat-comparable pairs.