Official health data are not only central to public governance and research, but subject of increasing public interest. This became particularly evident during the COVID-19 pandemic, in Sweden epitomised by weekly government agency broadcasts presenting data on infected, hospitalised, and deceased. Health registry data, however, are produced under slow and standardised control. Things unforeseen or beyond established health care classifications and procedures become excluded or marginalised. Associated biases of the ‘epistemic infrastructures’ of the pandemic (cf. Bauer, 2021) concern, e.g., ethnic communities, but also those infected that developed long-term debilitating Post-Acute COVID-19 Syndrome (PACS). A dedicated ICD-10-CM diagnosis code was not deployed until more than two years after the first notification of PACS-presenting patients at US hospitals (Pfaff et al., 2022), and its value for valid data production still remains contested. Patients in today’s datafied societies demand influence over what is considered relevant data (Dhruva et al., 2020). Consequently, PACS sufferers have not passively accepted the data gaps, but engaged in numerous counterdata activities; i.e. deliberate creation or repurposing of data to contest dominant narratives or highlight overlooked issues (Olojo,2024). This presentation uses a sociotechnical assemblage (Kitchin & Lauriault, 2014) and data journeys approach (Bates et al., 2016) to explore the politics and power aspects of PACS counterdata as dynamically shaped across contexts, actors, and systems. The analysis is based on observations, international co-research experiences, and 600+ questionnaire responses from Swedish PACS sufferers. In conclusion, potential societal and individual risks and benefits of PACS-related counterdata activities are presented.