I can see you don't add license notifications to the headers of the source files, but this tends to be the approach we take for copyright. I'm also not sure there is a very good alternative?
Instead of the monolithic copying of the full BSD-2 license with the NVIDIA copyright (which I appreciate might not be desirable), would it be a suitable compromise if we used the SPDX identifier, which looks like:
// Copyright (c) 1991-2021, NVIDIA. All rights reserved.
// Copyright (c) 1991-2021, UChicago Argonne, LLC and the PETSc Development Team. All rights reserved.
// SPDX-License-Identifier: BSD-2-clause
This would be for the main source files that we make any significant contributions to or author. I would be interested to hear your thoughts / ideas on this.