Purpose: While designing personally meaningful activities with data technologies can support the development of data literacies, this paper aims to focuses on the overlooked aspect of how learners navigate tensions between personal experiences and data trends. Design/methodology/approach: The authors report on an analysis of three student cases from a design study in which middle and high school youth assembled family migration stories using data visualization technologies with socioeconomic and demographic data. The authors used interaction analysis to examine how students responded to misalignments they encountered between their families' experiences and data trends in their models, drawing on the theoretical construct of epistemic data agency. Findings: This case analysis demonstrates ways in which students enacted epistemic data agency. Instructional support can help students deepen inquiry and avoid certain pitfalls, such as encoding data in unsound or misleading ways to support a particular story, while encouraging students to see themselves as an epistemic authority on par with data. This study opens pathways for future research that considers how data can shape personal narratives and how students can leverage their experiences in the stories they tell with data. Originality/value: The authors introduce the construct of epistemic data agency to describe the conceptual and material practices that reveal and shape students' relationships to the data. The descriptions of students enacting epistemic data agency in assembling data stories informs the understanding of how to better elevate and recognize students' efforts in relation to disciplinary norms and support deeper, meaningful student learning with and about data.