Galactic distribution of the OC samples studied in this Letter, sliced into logarithmic age bins. Left: pre-Gaia census using the MWSC catalogue (Kharchenko et al. 2013). Right: post-Gaia DR2 census, using the catalogue of Cantat-Gaudin et al. (2020). In each panel we show a 2D kernel density estimate with a fixed bandwidth of 0.05 kpc. For the MWSC, the dashed circle corresponds to the completeness limit of 1.8 kpc used in the literature (e.g., Piskunov et al. 2018); for the Gaia DR2 census, a sample limit of 2 kpc is used together with age-dependent completeness fractions indicated in each panel (see Sect. 2, last paragraph).