Voc is just the open circuit voltage measured at the terminals (plugs). “Nameplate” Voc is at standard test conditions (STC) of 1000 W/m^2, 25 deg C cell temperature, and a standard are mass/spectrum. The combo of 1000 W/m^2 and 25 C cell temp is not common in the real world in most climates, but still happens. Even relatively hot climates can have times in winter that exceed nameplate Voc if inverters turn off (making the panels go to open circuit).