In this paper, we present the results of a study that examines the role of data in nonprofit advocacy work. We conducted semi-structured interviews with 25 individuals who play critical roles in the data work of 18 different advocacy organizations. Our analysis reveals five key stakeholders in advocacy data work-beneficiaries, policymakers, funding and partner organizations, gatekeepers, and local publics. It also contributes a framework of four functions of data work in nonprofit organizations-data as amplifier, activator, legitimizer, and incubator. We characterize the challenges in data work that exist, particularly in widespread attempts to reappropriate data work across functions. These challenges in reappropriation are often rooted in participants' effects to enact data feminist principles from the margins of the data economy. Finally, we discuss how nonprofit institutions operate outside of the dominant data work goals known as the three Ss (surveillance, selling, and science) and propose a fourth S, social good, that is working to challenge the norms of the data economy and should be considered in research regarding the data economy moving forward.