Residuals of [Fe/H] as a function of Galactic longitude (ℓ) for different radial distances in the Milky Way. The plot shows the binned data (blue scatter) fitted with a polynomial (blue line) with a 95% confidence interval. Upper panel: data compared with the Model A+C3 predictions from Spitoni et al. (2023), which assume that, during the last 1 Gyr of disc evolution, all Galactocentric distances are co-rotations. The model is represented by a dashed green area, indicating the range of residual variations computed between 7 and 9 kpc. The residuals are calculated relative to the mean [Fe/H] value in each considered annular regions. Lower panel: same as the upper panel but showing the Model 3 Gyr predictions from Barbillon et al. (2025), where it is assumed that all Galactocentric distances are co-rotations during the last 3 Gyr of evolution. The model is represented by a shaded red area.