Abstract We evaluate the impact of new data in the annual release of SOCATv2024 on air‐sea carbon dioxide (CO2) flux reconstructions. Using the pCO2‐Residual and LDEO‐HPD methods, we reconstruct surface ocean fCO2 based on SOCATv2023 and SOCATv2024. For both products we find strong agreement in global mean air‐sea CO2 fluxes for 1990–2017, but a notable divergence beginning in 2018. Reconstructions based on SOCATv2024 estimate substantially less ocean carbon uptake compared to those based on SOCATv2023, with a global mean difference of 0.25–0.27 PgCyr−1 over 2018–2022. We find that flux differences are due primarily to large changes in the Southern Ocean where data from 63 cruises was added for SOCATv2024. Analysis with a model‐testbed indicates that these data, if unbiased, should substantially increase reconstruction fidelity. We conclude that there is high sensitivity of air‐sea CO2 flux reconstructions to the addition of data in poorly‐sampled regions.