@pajamawolfie
1. chapter 15 might have been in 2nd year. if every chapter is chronological: chapter 14.5 is new year, so chapter 15 might have been January ~march. and this chapter (24) is in April (new school year).
2. 'shijou-senpai' wasn't mentioned to be a 3rd year, she may have just been a famous graduate.
3. kishida's friends calling her senpai doesn't confirm that she is kishida's senpai, kishida may actually be his friends' 'senpai' and they just don't bother calling kishida 'senpai' because they're friends.