The excellent condition is due to hoarding vs. circulating.
Gold coins were very high value and thus not very useful for everyday transactions. Since people did not have bank accounts, they held savings in coins.
Gold coins were obviously the best coins to save - they were not demonetized. A bronze coin could be made worthless by a proclamation from the emperor. An
aureus might be held in savings for years, decades, or even generations.
Nero reduced the
weight of the
aureus, so older
aurei would have been hoarded and the
Nero coins spent first. Later
aurei were even lighter but by that time many of the
Nero aurei were already worn.
