Keeping powerful boons out of inventory when replaying

[Dynastol]

I played through Pathfinder Adventures once, and now want to start it from the beginning using different characters. For some reason high-powered boons (like level 6 weapons)  my last group collected are available in the inventory, and accessible for my level 1 group to equip themselves with. Is there a way to prevent this from happening?

[Ethics Gradient]

Not really.  The stash is shared space across all parties. 

Storage outside the party inventory doesn't really exist in the tabletop rules of the game, and was mostly added to help you trade between parties or swap characters around.  Since there is no per-party stash, your only real option to clean it out is to sell those cards off.