this is never happening - no physical items to represent currency for duping concern reasons.
~ @CluelessKlutz
This problem can be solved by creating a unique ID for every note. When the note is created, add its ID to the "existing_notes" table. When the note is redeemed, remove its ID from the "existing_notes" table. A note is only redeemable if its ID is in the "existing_notes" table. This way, even if I dupe a note worth 5 skulls with the ID of 3 and hold a total apparent note worth of 500 trillion skulls, I can only redeem one of these notes because they all have the same ID. You can also record instances where this check fails, and then catch people who tried and failed to dupe notes by redeeming an ID which was not on the "existing_notes" table.
on creation:
add UNIQUE note.id, note.value to EXISTING_NOTES
give player item with note.id and note.value
on redemption:
if note.id is in the EXISTING_NOTES table
- take the item from the player
- deposit note.value in the player balance
if note.id is not in the EXISTING_NOTES table
- the item is illegal, record this in a currencyLog.txt