Re/Os constraint on the time-variability of the fine-structure constant

We argue that the accuracy by which the isochron parameters of the decay ${}^{187}\mathrm{R}\mathrm{e}{\to }^{187}\mathrm{O}\mathrm{s}$ are determined by dating iron meteorites may not directly constrain the possible time-dependence of the decay rate and hence of the fine-structure constant $\alpha$. From this point of view, some of the attempts to analyze the Oklo constraint and the results of the QSO absorption lines are re-examined.