nah, that can't happen as it would be a "skip" race, so it's always 2 individual nags.
And UB, what I was attempting to do (though I now see is probably impossible) was this:

Possible scenarios
(1) System 1 the nag loses but system 2 the nag wins (what %)

(2)System2 loses but system 1 wins (what %)

(3) Both system horses lose (what %)

Given that system 1 has 70% losing S/R (overall)
and system 2 has 95% losing S/R (overall)