Where exchangeability fails at a measurement date, the entity estimates a spot rate aimed at the rate at which market participants would exchange in an orderly transaction under current economic conditions. It may use an observable rate unadjusted if that rate meets the aim, such as a rate available for another purpose (weighing whether multiple rates signal incentives or penalties, how narrow the permitted purpose is, whether the rate floats freely, and the frequency of updates) or the first rate available once exchangeability returns (weighing how long the gap is and inflation). Otherwise it may apply another technique, starting from any observable rate, including rates from mechanisms that would not give enforceable rights, adjusted as needed to meet the aim.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.