Those addresses are performing an indirect address of a Bit sub-element of a Word.
When N9:20 is equal to 0, those two addresses refer to N9:10/0.
When N9:20 is equal to 1, those two addresses refer to N9:10/1.
When N9:20 is equal to 2, those two addresses refer to N9:10/2.
Where else is N9:20 used in the program ? Because it's named "Sequence" it probably plays a major role in the program.
The way this logic works, whenever there are no Major Faults or Minor Faults, N9:0 through N9:6 are set to zero.
When there are no Major or Minor faults and one of the bits in N9:20/xx is true, the value of N9:20 is incremented by 1, and the bit that was set true in N9:10 is set back to false.