2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/1334We will briefly examine the following three issues related to the AGN synthesis models for X-ray background: 1) the possibility that absorbed AGNs evolve faster than unabsorbed ones; 2) the existence of the still debated population of luminous absorbed AGNs, the so-called QSO2s; 3) the behavior of the AGN density at a redshift above ~3.3 pages, 2 figures, to appear in the Proceedings of the 4th Italian Conference on AGNs, Mem SAItAstrophysicstext