The nature of the vector charmoniumlike states $\psi (4360)$ and $\psi (4660)$ has remained controversial for nearly two decades, and the very existence of the $\psi (4660)$ has recently been called into question: the high-precision BESIII measurement of the $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c^{-}$ cross section reveals a nearly flat line shape around 4.66 GeV with a nonzero value right at threshold, in striking contrast to the near-threshold enhancement reported earlier by Belle. In this work, we address this puzzle within a comprehensive S-wave coupled-channel framework for $e^{+}{e}^{-}$ annihilation in the energy region $\sqrt{s}\in [4.0,5.0]\mathrm{GeV}$. The formalism incorporates the open-charm baryon-antibaryon channels ${\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c^{-}$, ${\mathrm{\Xi }}_c^{+}{\overline{\mathrm{\Xi }}}_c^{-}$, and ${\mathrm{\Xi }}_c^0{\overline{\mathrm{\Xi }}}_c^0$ (organized via SU(3) flavor symmetry), the inelastic $\psi (2S){\pi }^{+}{\pi }^{-}$ channel mediated by the $\sigma (500)$ and $f_0(980)$ intermediate resonances, and the bare vector charmonium states $\psi (4360)$ and $\psi (4660)$, assigned as the 4S and 5S excitations. Short-range contact potentials constrained by heavy-quark spin symmetry are employed, the scattering amplitudes are obtained by solving the Lippmann-Schwinger equation. A combined fit to the Belle and BESIII data on $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c^{-}$ and $e^{+}{e}^{-}\to \psi (2S){\pi }^{+}{\pi }^{-}$ yields two poles, at $(4401.93\pm 16.96\mathbf{i})\mathrm{MeV}$ and $(4631.39\pm 62.96\mathbf{i})\mathrm{MeV}$, corresponding to the $\psi (4360)$ and $\psi (4660)$, respectively. By tracing the pole trajectories as the coupling to the bare charmonium states is gradually switched off, we demonstrate that both poles originate from the bare $4S$ and $5S$ vector charmonium states strongly renormalized by coupled-channel dynamics. In particular, the $\psi (4660)$ emerges as a broad resonance located about 58 MeV above the ${\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c^{-}$ threshold—its flat experimental line shape is a direct consequence of this threshold interplay, and provides evidence for its existence. Our conclusion is robust against the variation of the regularization cutoff.

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