Can you please synthesize and summarzie the following passage about the limitations of the cox model.

The Cox hazards model differs from the classical regression model because it introduces time-dependent censored variables for cases when the analyzed end point does not occur during observation. As a result, it is not possible to calculate the so-called "model residuals", i.e. the differences between the real and expected values of dependent variables. However, it is possible to check the assumptions in a non-parametric hazards model if one uses Schoenfeld residuals, test 2 and the Rho coefficient of rank correlation between residuals and time. Obtaining a horizontal regression line of residuals across the time axis confirms the proportionality of hazard (Abeysekera et al., 2009; Grambsch et al., 1994; Keele, 2010; Schoenfeld, 1982; Winett et al., 2001). Unfortunately, this important assumption has been checked and properly reported in very few scientific publications.

It is improper to use a simple Cox regression model with regard to the violation of proportional hazard assumptions as it can lead to false deductions. Using a regression model with stratification of variables (the so-called stratified model) or an extended regression model with time dependent variables, which is one of the so-called non-proportional hazards models, is recommended.