Natural history collections have existed for considerable time, and their contribution to research has been discussed and praised in recent decades. In scientific literature, however, there is a general lack of records from private and other small collections. Here, we show that these collections represent a highly valuable resource for research, because they may include an important number of specimens with a broad range of origins. We used the Iberian lynx to demonstrate that the wider and less-biased representation of specimens often found in these collections allows for additional and better inferences than those that are drawn exclusively from large institutions. Locating small zoological collections, however, is very time consuming, and, unfortunately, such collections often disappear quickly, putting their long-term persistence at risk. We propose that authorities, researchers, and curators work together to locate and legalize these specimens and facilitate their inclusion in public databases and, eventually, in larger natural history museums that will ensure their existence in perpetuity.