Any time Kas blows a load in your pussy after the tutorial, she can get you pregnant. If the text says she doesn't, then she doesn't. You should read her actual conversation about imps, maybe you'll see why she's reticent to do so. Especially considering what just happened downstairs.
I, uh, did. Read it that is. I fully understand the in-story reasons she hates imps and might not want to make more or make the MC a mother of them.
This is out of story. Frankly I like the imp-birth/corruption scenes and wanted to see more. The previous imp-birth scene heavily implied there would be future ones. Which leaves me with questions. For one, you said "any time Kas blows a load in your pussy after the tutorial, she can get you pregnant."
Assuming that dreams don't count (correct me if I'm wrong of course), is there another time where she can impregnate you? The first time she blows a load in the MC (edit: first time after the tutorial), I believe it's a guaranteed pregnancy (or at least it's never not been one for me, so long as the MC isn't already pregnant). Other than the dream and I think the holiday interaction, I don't remember any other time she can impregnate you. In the Winter City, even after she blows a load in the MC, she then says a line about how she doesn't want the MC to give birth to imps and does something that presumably prevents it.
Am I misunderstanding something? Is there a chance for an imp pregnancy in this scene but it's just not guaranteed (so RNG isn't on my side basically)?