Temporal evolution of NZPs. Black errorbars: HARPS-post SERVAL NZPs. Cyan dots: Stellar zero-point subtracted RVs of all RV-quiet stars (weighted RV rms scatter <10 m s⁻¹). Red boxes: NZPs that were calculated with too few (<3) RVs. Red circles: NZPs with too large uncertainties (>1.2 m s⁻¹). Magenta circles: significantly deviating NZPs. The RVs in the red-marked nights were corrected by using a smoothed version of the NZP curve, which was calculated with a moving weighted average (21-d window). For the ten significantly deviating NZPs, we adopted their individual (unsmoothed) NZP values, regardless of their uncertainties. Green dots: NZP values that were eventually used for the correction.