Today's topic is using family histories and genealogies. These can be great tools, but can also be a royal pain!
1] Look at the publishing date. The earlier the book was published the more likely that you will find errors. The author[s] were at the mercy of the technology of the time. Writing letters was the method of communication early on and travel to the sources of the material was not convenient for the researcher. Family lore was often given as fact. Family members were overlooked. Sources were limited.
2] Some genealogies were a disaster! Fraudulent genealogies were a problem from about 1880 to 1920 or so. Two of the primary culprits were Gustav Anjou and Horatio Gates Somersby. If you wanted to be related to a famous person with your surname or have connections to European nobility, it could be done with a few creative pieces of "evidence." There are a few webpages dedicated to listing fraudulent genealogies, check them out.
Other family histories were well-meaning, but poorly researched. In the early Lockwood Geneaolgy, nearly all Lockwood descendants were assigned to Robert Lockwood. His brother, Edmund, was all but ignored. Donald Lines Jacobus, an early noted genealogist, debunked the Lockwood work. As it turned out Edmund was the progenitor of the vast majority of the American Lockwoods. Harriet Woodbury Hodge's Some Descendants of Edmund Lockwood corrected errors in the original genealogy.
It was, unfortunately, common for authors to omit children or assign them to the wrong parents. The researchers were at the mercy of those people who supplied them with information. Wills, deeds, bounty land settlements and other documents that did not specify relationships led researchers to make incorrect assumptions as to how the people named in the documents were related. Two generations of my Pralls were mixed up for years, until more extensive research uncovered the true relationships. The St. John Genealogy had Samuel St. John as the son of Mathias III. An examination of deeds has led to the belief that Samuel was the son of Mathias II. The origins of the St. Johns in Europe is a whole other issue!
3] More current genealogies should be more reliable and contain information unavailable in the late 19th or early 20th centuries. But, don't bet on it. Rehashing detail from a century old family history can be very common.
1] Check the sources cited in the genealogy and, if possible, consult those sources for accuracy and reliability.
2] Utilize documentation to form your own conclusions about questionable issues. [The St. John item from above, for example.]
3] Confirm details from earlier genealogies by consulting more recent sources [census, death records, town records, court and probate records] made available since the genealogy was published.
4] If another genealogy is listed as a source, consult the other genealogy for reliability and sources used.