Venn diagram showing: the subsamples of spectroscopically confirmed Type I and Type II AGN (spec. Type I, 225 sources, and spec. Type II, 122 sources, respectively; these two subsamples, by definition, do not overlap); the sample of sources classified as AGN on the basis of their X/O diagram (X-ray, 605 sources); the subsample of AGN selected after their MIR properties (Donley et al. 2012; MIR, 225 sources); and the subsample of objects classified as AGN based on their optical variability (De Cicco et al. 2021; opt. var., 301 sources). We caution that the area covered by each region and the corresponding number of sources are not related. These five subsamples of sources combined together constitute the main sample of AGN used in this study.