If the group believed themselves to be 17 years old, Cordelia would have already known Angel as they met when she was 16. However Cordelia does state at the beginning of the ordeal that it could be a "sophomore hazing prank" which, if she believed herself to be a sophomore, could be before she met Angel, but that would also mean that Cordelia is younger than the rest of the group as sophomores are between 15 and 16 years old.
When Connor appeared as a teenager in season 3, it is mentioned that he is sixteen years old, but in "Spin the Bottle," Cordelia says he is 18. It's impossible for him to have aged two years in a span of roughly three months without making another travel between dimensions.