  In the paper we recalculate and discuss high-precision theoretical
predictions for cross sections of the process $e^+e^- \to Z Z$. We assume a
complete one-loop implementation and a possibility of estimating the initial
state polarizations, as well as the full-phase calculation. Numerical results
are provided by our Monte-Carlo tools MCSANC integrator and ReneSANCe generator
for typical energies and degrees of polarization of ILC and CLIC projects in
two $\alpha(0)$ and G$_{\mu}$ electroweak schemes.
