Simulation-based scoring of mask defects is useful for technology nodes of 180 nm and below since wafer shapes can be quite different from those on the mask, and therefore not every defect has printing significance. An important issue for simulation-based scoring is calibrating the resist model. Calibration data is scarce for a variety of reasons, among them, (i) the mask shop is not privy to it, and (ii) the reticle-inspection machine may not visit calibration locations. Specifically, while is relatively easy to obtain the target critical dimension (CD) - the intended value of the smallest wafer CD for that mask, the cutline position for that target CD is uncertain. This work focuses on calibrating the simplest of resist models, a threshold, using only knowledge of the target CD. It quantifies the uncertainty in target cutline position with a probabilistic treatment. This shifts the question from, "What is a good threshold?" to, "What is NOT a bad threshold?" The answer is a range of thresholds that does not print sub-resolution features, and that does not grossly distort the ratio of inspection-image CD to wafer CD. Defect dispositioning is then based on the most pessimistic printability score for that threshold range. Given the uncertainty in resist-model calibration, it is appropriate to be conservative and assume the most pessimistic resist threshold.