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Our group reported that the polyoxometalate Na₁₀[Co₄V₂W₁₈O₆₈]·26H₂O (Co₄V₂) is an active water oxidation catalyst and provided characterization of this system (J. Am. Chem. Soc. 2014, 136 (26), 9268). Two recent publications called into question the stability of Co₄V₂, one noting the miss-assignment of a ⁵¹V NMR peak (Inorg. Chem. 2016, 55 (11), 5343) and another providing additional stability studies (ACS Catal., 2017, 7 (1), 7). We report here solution studies that further clarify stability limitations in this system by locating the correct ⁵¹V NMR resonance of Co₄V₂ and the other V-containing species present. Furthermore, we demonstrate that the observed catalytic activity cannot be explained simply by Co(II)_aq, but arises from multiple active WOC species in solution. Key points about investigating such complex equilibrating aqueous catalyst systems are addressed.