Hertzsprung–Russell diagrams. Initial mass is color-coded (between 9 and ∼500 M_⊙); dots mark every 10⁵ yr of evolution along the stellar models. Dashed black lines represent interpolated tracks (up to 500 M_⊙); brown crosses mark the phases in which the direct extension method (Sect. 4) has been applied. For details about the models and their postprocessing, see Sects. 2 and 4, respectively, and for details about the interpolated tracks, see Sect. 3.