Density maps of the observational HRDs of two dataset A sub-samples with relative parallax uncertainties better than 10%: for sources with C′ < 1.02 in the top panel (subset F in the text) and for sources with 1.11 < C′ < 1.3 in the bottom panel (subset L in the text). The density maps are plotted on top of Gaia DR2 sources (constant and variable) with relative parallax uncertainties better than 2.5% (light grey in the background). Density goes from low in red to high in black on a logarithmic scale.