We show that recent resistivity measurements on radiation-damaged tetrathiafulvalenium-tetracyanoquinodimethanide (TTF-TCNQ) are consistent with Matthiessen's rule appropriately applied to strongly anisotropic conductors. The effect of the damage is simulated by a model broken-chain network whose calculated resistivity agrees closely with experiment. The effective defect resistivity that appears in Matthiessen's rule includes an interchain component and is therefore temperature dependent. The same model also reconciles the low-temperature non-linearities observed in damaged samples with hot-electron theory. © 1979 The American Physical Society.