Equations of state that are based on the lattice-statistics approach use Guggenheim's quasi-chemical approximation to describe the non-randomness in the mixture due to the energetic interactions between the molecules. For ternary and higher-component systems the non-randomness expression is complex and requires an iterative calculation procedure. Generally phase equilibrium calculations are based on equating the chemical potential of the components in the equilibrium phases. Alternatively one can use equality of the fugacity coefficients. We have shown that the non-randomness parameters play a negligible role in the application of the GCLF-EoS model (based on the Panayiotou-Vera EoS). Therefore, the non-randomness parameters can be omitted from many phase equilibrium calculations, and the computation efficiency significantly improved.