For instance, suppose a user buys a perpetual that rolls over every 24h. In the same transaction, the pool takes a unit of the "opposite" derivative onto its balance sheet. A week passes without anyone interacting with the protocol. On-chain state will still show that both the user and the pool own one derivative in the original vintage. However, in that time, 7 rollovers would have occurred, and the "economic reality" is that both user and pool de facto own different quantities and in a newer vintage.