In 1972 the Smithsonian Institution published this book by former NAVA president Grace Rogers Cooper, Thirteen-Star Flags: Keys to Identification. It contains a wealth of information on the early history of US flags and surviving examples, and how to detect impostors. And the public domain full text is available online!
Cooper (1924-2004) was an important American vexillologist and textile expert, serving as a curator at the Smithsonian Institution. She was the first woman to serve as NAVA’s president from 1983 to 1986, and went on to edit NAVA News from 1987-1995.