One thing I was reminded of when writing A Governesses Guide to Marriage was that a duchess remains a duchess when her husband dies and she doesn't become a dowager duchess unless the new duke has a wife, or if he is single—when he marries.
Another fact I found out while writing was that Regency constables are supervised by the magistrate, and the constables are paid for by the person needing the assistance.
The Beau Monde writing group shares information about Regency lifestyles and I've been fortunate to be a member of that group for the last five years.