A fundamental part of my worldbuilding is that these stories are set in an alternate Victorian era. I try to use actual history and historical people as much as possible. When something I’ve changed makes a historical person or event untenable as they actually were, I try to change things in a way that makes as much sense as possible, and, mostly, allow the alternate history to drive the story. If I really want the story to go in a particular direction, I’ll tend to go back and modify things in the “past” (from the point of view of that story) so that my desired story direction makes logical sense.