I mean the spot price at the moment of redemption.
Yes, that would be the external spot price which I keep insisting matters very little. The price of a sale is decided by the buyer and the seller of the contract. They have an incentive to meet at the external spot price, but the incentive is small.
But when the contracts are redeemed automatically (before becoming "insolvent") and when is decided who was right in his bet and how much has to get from the other's party escrow is when the external spot price matters. If it didn't matter, we didn't had to input information from the markets.