Accuracy of Spirit vs. Accuracy of Detail
Getting the spirit of an era right matters more than getting every date correct. Readers forgive an anachronistic button. They don't forgive characters who feel like 21st-century people in period costumes. The spirit of an era is its underlying logic: what people believed about death, god, gender, hierarchy, and obligation. When that logic is wrong, the book feels like a costume drama. When it is right, readers can forgive small errors of detail because the world feels lived-in and true. Research the logic of the period first; the details follow from the logic.