No wonder there were new details that didn't follow or in the original game event, the Mangaka was never planning to adapt the game event. With the appearance of Kazuradrop, an Alter Ego that haven't been added to FGO yet, we can say that this manga is definitely following an "Alternative" route from the game event, rather than an "Adaption" of the game event. Though....if "Kazuradrop" appeared in this manga, then DW might probably add her in FGO in the future, and that mean we will probably get a new S.E.R.A.P.H event for Violet and Kazuradrop, since there is never a 3rd re-run for an event after all.
Or maybe the Mangaka just want to randomly add Kazuradrop in for fun? Type-moon allow that?