The NO anneal has been shown to effectively remove 99% of defects in SiC based devices. However, the details of interactions of NO molecules with amorphous (a)-SiO2 and SiC/SiO2 interface are still poorly understood. We use DFT simulations to investigate the NO incorporation energies in a-SiO2, and how these are affected by the steric environment. The results explain the ease with which NO molecules incorporate into a-SiO2 and give an insight into the diffusion paths they take during annealing. We highlight the importance of exhaustive sampling for exploring NO diffusion pathways.