Does research output grow, or does database coverage grow? Data-source and retrieval biases in measuring institutional research output (2016–2025)

Institutional bibliometric assessments often read growth in indexed output as growth in research production, although the expansion of database coverage and the retrieval method can alter the estimated volume and growth. This study examines both effects at the Universidad Católica de Temuco (Chile), 2016–2025. Scopus, Web of Science and OpenAlex are triangulated; retrieval by institutional identifier is compared with retrieval by currently affiliated authors; attribution, publication dates and duplicates are verified in OpenAlex; and the historical coverage of Scopus is reconstructed from record loading dates. Annual growth ranges from 13.1% to 17.7% depending on the source, and retrieval by current affiliation omits between 19% and 26% of the 2016–2021 output. Of the verified articles, 22.7% are outside Scopus and Web of Science, with a predominance of Spanish, diamond open access, and the social sciences and humanities. The decline in the share published outside Scopus is mainly explained by the subsequent inclusion of journals in the database, not by a shift toward journals already covered in 2016: Scopus shows annual growth of 15.2% for output that grew at 13.1%, and with its 2016 coverage it would have shown 11.6%. In OpenAlex, 135 works (13.1% of those absent from the commercial databases) lack verifiable attribution. The contrast with an emerging Ecuadorian university shows a similar concentration of citations, but not the same growth pattern.