The low process stability of laser welding of copper with near infrared lasers leads to the requirement of precise input data for process control and meaningful simulations. But at the same time, available datasets of temperature-dependent reflectance or absorptance for near infrared lasers on copper do not show good agreement between the different sources and often do not include the fusion process, which is of crucial importance for realistic laser welding simulations. Additionally, most of the datasets are only calculated. We recently performed temperature-dependent reflectance measurements on copper using a near infrared laser. The measurements revealed a reflectance drift, which is induced by the setup behavior during heating, and the time-dependence of chemical reactions like the redox-reaction as possible error sources. In this study, we performed experiments on laser melting as the fundamental process of laser welding, and we conducted corresponding simulations using our measured reflectance values for oxide-reduced and for untreated copper. We then compared the simulations with the experiments to estimate the accuracy of our reflectance measurements. To provide context, we also conducted the same simulations using reflectance datasets from other authors. In a second step, we corrected our reflectance data with respect to the reflectance drift and adapted the effects of redox reactions to the conditions of our laser melting experiments. Using the resulting reflectance curves, we achieved an improved agreement of simulation results and the experiments over a range of different test cases, without the necessity of correction factors in the simulation model.