Time-dependent changes of the reflectivity factors obtained from WDR measurements. Black points show the average reflectivity factors for each instrument epoch. Blue, orange, green, and red points show the individual reflectivity factor measurements for each telescope. Curves of the same colors represent a spline interpolation, which removes outliers. The first point (early 2012) is extracted from the simulations and it serves as the reference for the calculation of the reflectivity factors, therefore adopting a value of 1 as reflectivity factor. We note that a value of the reflectivity factor slightly greater than 1 just means that the reflectivity at that time was slightly higher than at the time where simulations were produced.