  Large-scale $\textit{ab initio}$ calculations of the electric field gradient,
which constitutes the electronic contribution to the electric quadrupole
hyperfine constant $B$, were performed for the $5s^25p6s$ $^{1,3}\!P^{\rm o}_1$
excited states of tin, using three independent computational strategies of the
variational multiconfiguration Dirac-Hartree-Fock method and a fourth approach
based on the configuration interaction Dirac-Fock-Sturm theory. For the
$5s^25p6s$ $^{1}\!P^{\rm o}_1$ state, the final value of $B/Q =703(50)$ MHz/b
differs by $0.4\%$ from the one recently used by Yordanov ${\it et~al.}$
[Communications Physics ${\bf 3}$, 107 (2020)] to extract the nuclear
quadrupole moments, $Q$, for tin isotopes in the range $^{(117-131)}$Sn from
collinear laser spectroscopy measurements. Efforts were made to provide a
realistic theoretical uncertainty for the final $B/Q$ value of the
$5s^25p6s\,^{1}\!P^{\rm o}_1$ state based on statistical principles and on
correlation with the magnetic dipole hyperfine constant $A$.
