Plot hole: How did Buffy know where to find Riley at the end of 'Into The Woods'? He told her he was leaving with the army, but he never mentioned the helicopter pad. (00:40:30)
Plot hole: When Buffy talks to Xander at the end and he tells her to stay with Riley, she mentions that he is going at midnight. But earlier in the episode, Riley doesn't tell Buffy he is going at midnight, he says "Transport's leaving tonight" first, and at the end of the conversation he says "Unless you give me a reason to stay, I'm leaving tonight". Nowhere in this episode does he tell Buffy that he's leaving at midnight.
Chosen answer: From what we see in the series, certain girls are identifiable as potential Slayers - Kendra clearly fell into this category. The identification method is presumably mystical in nature, but the Watchers' Council are pretty effective at that sort of thing, so they're quite good at tracking down the potentials ahead of time. Not perfect, though - it does appear that Buffy herself may have slipped through the net - certainly she had no inkling of what she was until she'd already taken on the role of Slayer. It is possible, however, that this was actually cultural - an American family would hardly be likely to turn over their daughter to some strange man for 'training', so the Watchers might have chosen to keep an eye on her covertly, whereas some other cultures (like Kendra's Jamaican parents) might be more willing to believe.
Tailkinker ★