Aging structures need repairing if their lifetime is to be extended. If the structure has been monitored before and after repair, the information from both configurations can be utilized. The data before repair include the environmental or operational influences, whereas the data after repair represent the current structural condition. Also, if damage is proportional to the worked modifications, its extent can be assessed solely from the measurement data; no finite element model is needed. The proposed method is verified with a numerical model of a vehicle crane.