I don't think it's actually possible to get the Brittany pregnancy announcement interlude in which she knows you're the father, BrittPregAfternoon087cStart2.
It requires a fairly early impregnation. The pregnancy checks...boy, tracking time in this code is a headache, but it looks like practically all the pregnancy checks are triggered in Math087Finished1, which only fires on Wednesday the 14th, which requires her pregnancy status be at 7+, which means she was impregnated at least week prior on Thursday the 8th. But the early opportunities to impregnate Brittany are very few, and none of them that I can see are -known- pregnancies. There's when she's wasted (unknown father), when you've stopped time (unknown father), and...that's it, I guess, in the early period?
So not only is that scene apparently unavailable, but it's also the earliest of three places that can set britt_girlfriend, the other two being basically in the 'endgame' at the sorority party or, much more obviously, the picnic with her. So earlier effects of girlfriend status with her are, I think, unobtainable.
Of course, 'fixing' such an issue is not readily achieved, since it's more a design matter than any specific error. Shame, though.