Distribution of 5100 Å (top panel) and radio (bottom panel) luminosities vs. redshift for the NLS1 subclasses. RQ-NLS1 (blue dots) are mainly located at low z. The few sources at higher z are among the most luminous: the radio flux sensitivity only allows us to observe the peak of the iceberg. RL-NLS1 (red dots), instead, are more evenly distributed in luminosities and z; thanks to their larger radio flux, they are less affected by this observational bias compared with RQ sources. They are missing in radio surveys from higher redshift than their RQ counterparts.