Corrected entry: On both occasions in season 7 prior to "Chosen", whenever blood is spilled on the seal of the hellmouth, an ubervamp is brought out as the seal opens (e.g. when the First bleeds Spike; when the demon girl bleeds Xander). But, in "Chosen", when Buffy and the Potentials cut their hands to open the seal, no ubervamps are waiting to come out. Instead, the seal opens to reveal a set of stairs that lead them down to where the ubervamps are. That is the only way the Slayers could get to the vamps to surprise them, and the only way the whole ending with Spike could happen, but it isn't consistent with the rest of the season and what happens when blood is spilled on the seal.
Corrected entry: For most of Series 7 there is a girl from Hong Kong among the Potentials. No one can speak Cantonese and she doesn't speak any English, so how did Giles convince her to get on a plane with him and fly to America? She wasn't sent by her watcher - Giles states very clearly in 'First Date' that she never had a watcher, and in 'Potential' Buffy mentions to the others that 'Giles has gone to Hong Kong to find the Potential there.'Shay