Traditionally, the bibliometric community has relied heavily on secondary data sources, most prominently the Science Citation Index. By analyzing three key journals, we detected trends in the data sources used over a 45-year period (1978-2022). The historical analysis of data sources reveals a consistency in the materials used as well as bursts of new materials and approaches. On a larger scale, the pattern is stable with Web of Science and Scopus dominating, but this might be about to change. The complexity of the research performed in bibliometrics does not seem to increase as a vast majority of studies use one or two types of data sources despite the increasing availability of data. A more detailed analysis detects trends in the use of data, as represented by patent analyses in the 1980s, webometrics in the late 1990s, and altmetrics in the 2010s. Overall, the paper provides an analytical overview of current and historical data sources used in bibliometrics, which may guide and inspire further research. The question remaining, however, is how the current emphasis on open sources will transform the field in the future: are we entering the great wide open, or will established proprietary databases remain a dominating source?