With litepacks alone, it was only possible to take a small portion of the treasures in the vault. It was filled with so many good things that it was hard to believe the Old Duke accrued it all within the scenario.
However, the vault only came into existence during the scenario. The Old Duke must've sensed it through the same perception Sequence he used to spot Gio.
Most of what was found inside came from the scenario. It looked like a lot of it was provided by the forces under him as some sort of tribute.
Another portion of it, however, definitely came from outside. The vault cards in the corner didn't exist as a form of currency in the period that the scenario was based in, and some of the resources and raw materials were also staples of the modern world.
'The most likely case is that he has something equivalent to a Storage Hole and he dumped the stuff inside in here.'
