1. An optical proximity correction method, comprising: providing a radiation-patterning tool substrate; providing a first dataset which defines a first radiation masking pattern for a first part of a radiation-patterning tool formed from the substrate, and providing a second dataset which defines a second radiation masking pattern for a second part of the radiation-patterning tool formed from the substrate; performing OPC calculations on the second dataset and modifying the second dataset based on the calculations, the OPC calculations of the second dataset utilizing at least a portion of the first dataset but not modifying said portion of first dataset; and forming a pattern supported by the radiation-patterning tool substrate utilizing the modified second dataset.