Courtesy Titles can be fun or sheer hell, depending on your Point of View.
Here's a real life example: The 8th Duke of Devonshire died without issue. His heir was the eldest son of his brother, Lord Edward Cavendish, who had predeceased him. As long as the 8th duke lived his heir presumptive (Victor Cavendish) had no title, nor of course had his two brothers. But when Mr Victor Cavendish succeeded to the dukedom, his brothers became Lord Richard and Lord John Cavendish. His mother, however, remained Lady Edward Cavendish.
It is interesting that even though Victor would have inherited had his father, Lord Edward, succeeded to the dukedom, these privileges cannot be claimed as a right. They are given by favour of the Crown and warrants are granted in such cases only upon the recommendation of the Home Secretary.
(I am using capitals as used by Titles and Forms of Address. The use of capitals where royalty and the nobility are concerned in fiction is food for a whole other post.)
I have difficulty with hereditary barons and baronets. Barons and Baronesses make up the fifth and final grade of the peerage, ie the lowest in rank. The confusion possibly comes from the Scottish peerage created in Scotland before the Act of Union in 1707, and the installation of Life Peers; but before we digress, lets look at English barons.
All of this rank are known as Lord or Lady with the exception of peeresses in their own right who may choose to be called Baroness. The title is sometimes territorial, sometimes a family name and sometimes something made up for the purpose. An example might be Baron West, with a family name of Sunderland. In speech these people are addressed as lord and lady or baroness. In writing I should address them as My Lord, or My Lady. If I know them personally I might write Dear Lord West or, if I know them really, really well, Dear West.
A dowager baroness is the earliest surviving widow of a peer. If he had a second or even a third wife, they are distinguished by the use of their forename before the title. The former wife of a baron uses her forename before the title. So there is sense in getting it right. If I'm introduced to Lady West, Lady Lavinia West, the Dowager Lady West or Daphne, Dowager Lady West, I ought to be aware of their status within the family.
Enough for one day? I think so.