https://en.m.wikipedia.org/wiki/Mausoleum_of_the_First_Qin_Emperor

By X means before the first day of X

"Excavate" : at least one artefact that the Chinese government claims comes from the burial chamber or sarcophagus (or nearest applicable concept) of the emperor has been shown to the world visually. It doesn't need to be on display, but there must be a photograph of it.