As an index and abstract to pre-1850 Connecticut vital records, the Barbour Collection is popularly used in lineage society applications as “proof” of birth, death and marriage. (For history of the collection and for information on its three “formats,” visit https://connecticutroots.org/2023/07/28/are-there-multiple-versions-of-the-barbour-collection/.) The collection is generally considered to be reliable.
Yet, as genealogists, we want to be able to make the judgment of whether a source is reliable for ourselves. One of the questions we ask is if the source is original or derivative (recopied). Working with an original source allows us to work with the information as originally provided. Working with a derivative means that we risk working with some degree of copying errors. Humans make typos, especially when copying a lot of information at once.
The Barbour Collection you’re reviewing at online is definitely a derivative source – sometimes a many degree derivative. Each new version was created by recopying a prior version. Of the online versions, the Slip Index (https://www.familysearch.org/search/collection/2843390) is likely closest to the original.
In some towns, the sources used to create the Barbour were not the originals. For example, the volume for Durham includes only births, baptisms, marriages, and deaths that were printed in Fowler’s The History of Durham. The compiler never reviewed the original records. To determine which sources were reviewed, look to the introduction of the appropriate 1930s volume, accessible from FamilySearch at https://www.familysearch.org/search/catalog/295370?availability=Family%20History%20Library.
Connecticut Roots by Charter Oak Genealogy 
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