Relative PSF error, at observation resolution, as a function of the number of training stars. The baseline is set to the performance of the approximate PSF trained with 50 stars and ground truth SEDs (dark yellow). The subsequent PSF models (blue points) are trained using the 50 baseline stars in addition to increasing numbers of stars with SEDs assigned by our PSF-aware classifier. The error bars represent the standard deviation of the relative errors of the test dataset. The green dashed line shows the idealised minimum relative PSF error that can be obtained when using 2000 stars with ground truth SEDs, and the green shaded area represents the standard deviation of the relative errors.