I didn't pick up on it either. The main reason I stress it is because when I did rewatches of the early seasons I wanted to prove the Bander crowds wrong, and that lasted for about two minutes. The evidence is just overwhelming when you watch with that question in mind.

Your last sentence is my take on what happened. There are still pings on it in season two and season three -- probably for continuity. If I had to guess, I'd say that the story line got dropped when they decided to turn Angel into a hero of his own series. Mid-season 2. But even in early season 2 it feels like the X/C B/A is a mismatch that's supposed to eventually get reswapped. (I'll try to stress this as I go forward, but there's a lot of Cordelia - Buffy mirroring, so the set up for that switch seems plausible to me).