The same complications arise when measuring externalities, since external costs can be defined precisely only with reference to a specific problem (the internalisation of costs through taxes, for instance; it can also be useful to measure external effects prior to making an investment or to taking action in many other areas).
It is also important to specify the model that is being used (in the case of internalisation, prices can be calculated using a Ramsey-Boiteux budget equilibrium constraint model, or the Shapley value).
Every problem and every policy response will place a different value on social cost.