For the engineering of nitrogen-vacancy (NV) centers in diamond, vacancies have been introduced locally into a type Ib diamond (100–200 ppm nitrogen content) by implanting argon ions from a sub-500 nm focused beam. At an acceleration potential of 12 kV, different charge states (Ar n+, n={1,4,8,11}) result in kinetic energies of 12–132 keV. NV-centers were formed by a subsequent annealing step. A wide range of fluences from around one ion to several hundred ions was implanted per spot. It was found that, on average, between 0.04 (12 keV) and 0.79 (132 keV) NV-centers are created from the vacancies of a single implanted argon ion, depending on the ion energy, but not on the fluence. The different number of vacancies created at each energy alone cannot account for the difference in NV-center yield. However, the probability of a given vacancy to diffuse to the diamond surface during annealing, where it cannot contribute to NV-center formation, was simulated and can fully explain the NV-yield behavior. With this model, an upper bound of approximately 300 nm for the diffusion length of a single vacancy was found for an annealing temperature of 800 °C.