Talk:Yumiya Rakko/@comment-173.171.141.5-20190418060201/@comment-25431873-20190418184631

“''Oh, this is that super plan of School’s. But I was super sure we had taken out their assassination sniper three days ago…''” - OT15 chapter 2 part 2

So Yumiya died between her defeat to Frenda in Railgun and October 9. It's less of a retcon and more just weird why Kamachi had her survive the fight in Railgun in the first place.

Personally, this is why I never use the Bakatsuki calendar, since it's made up mostly of guesses and has no citations or explanations for the choices of date placement, which might explain your confusion.