Are the busts of Roman leaders like Caesar taken from death masks or are they impressions crafted from contemporary descriptions?

by Beccorban

Basically I am asking how accurate the busts of figures like Sulla, Marius, Pompey, and Caesar are. Is there a definitive answer or is it more speculative?

Cataphractoi

Follow up query; Octavianus, Trajan and even Constantine I had a bust, however Basil II did not. At what point did they stop producing busts for each emperor and move towards using mosaics like that of Zoe and Constantine IX or Ioannes II Komnonos at the Hagia Sofia?