Upper panel: Comparison of the resulting oxygen abundance of old stars (> 3.5 Gyr) in the modelled disc with the oxygen abundance of old PNe from Bhattacharya et al. (2022). Each vertical line specifies the mean values of the two datasets. Shaded regions represent the standard deviation (1 × σ) of each dataset. The y-axis [left] is the mass percentage of stars older than 3.5 Gyr in the model. The PNe are plotted according to their number counts in the survey (y-axis [right]). Lower panel: Same as the upper panel but reporting the comparison between younger stars (< 3.5 Gyr) in the model and young PNe.