Your schematic shows when the Advance Unit will fire. On the left side is a normally open switch on the X relay so nothing happens unless the X relay has fired. On the right side are three Score Motor switches which each let a pulse into the circuit whenever the Score Motor turns through one cycle. So assuming the X relay has fired there are three ways to step the Advance Unit:

1) the pulse from the Score Motor 4C switch will always step the Advance Unit
2) the pulse from the Score Motor 3B switch will step the Advance Unit if the V relay has fired in 3 ball mode
3) the pulse from the Score Motor 1B switch will step the Advance Unit if the V relay has fired and either
..3a) the Advance adjustment is in the Liberal setting or
..3b) the Y relay has not fired and in 3 ball mode

One thing the schematic does not show is the Motor Sequence Chart which would show when the three Score Motor switches fire relative to each other.

/Mark

Domino Domimo lights (resized).jpg
It looks like when the Advance Unit is reset and at position 0, the 5 domino should be on, unless the game is tilted.

/Mark