SPDX identifiers in the kernel

True, but the problem with the BSD licences are that the *terms* of the licence differs depending on the copyright holder (as the original BSD licence explicitly mentioned "University of California, Berkeley" and other copyright holders replaced that with their own name when they released code under an equivalent license).

For example, the *only* difference between the *terms* of BSD-2-Clause and BSD-2-Clause-NetBSD are these two phrases:

(1) "THE COPYRIGHT HOLDERS" <-> "THE NETBSD FOUNDATION, INC."
(2) "THE COPYRIGHT HOLDER" <-> "THE FOUNDATION"

>> Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
>Templatized or boilerplate copies of the license are insufficient to meet this requirement.

Obviously using SPDX to *identify* the licence does not absolve you of the responsibility to also *comply* with the license. But SPDX license identifiers *can* make it easier to do so.

Consider the following hypothetical project of 5 source files. Note that file01.c and file02.c have different copyright holders and thus different copyright notices, but both are under the same licence, so you only need one copy of the license *terms* (located in the file LICENSE.BSD-2-Clause). However, file03.c is copied from NetBSD and are thus under a slightly different license. Therefore it does not only uses a different copyright notice, but also a different SPDX license identifier and a separate copy of the license terms (this time located in LICENSE.BSD-2-Clause-NetBSD). Note that LICENSE.BSD-2-Clause and LICENSE.BSD-2-Clause-NetBSD only differs by 4 words, but (as you said) some sort of template would not actually comply with either license, and you therefore need to carry both versions. Next is file04.c which is copied from FreeBSD, which is under another slightly different license, and thus a third SPDX license identifier and a third license file. And finally we have file05.c which contains parts copied from NetBSD, parts copied from FreeBSD, and parts written by me, which means that to use this file you need to comply with both the NetBSD license and the FreeBSD license (which fortunately are compatible with each other, you just need to keep both license files around to comply with both of them at the same time). All in total there are 5 source files with a total of 6 copyright notices, but thanks to the SPDX license identifiers we only need one copy each of the 3 license terms.

========== file01.c ==========
// Copyright (c) 2012-2016 Joe Random Hacker
// SPDX-License-Identifier: BSD-2-Clause
...

========== file02.c ==========
// Copyright (c) 2017 Jon Severinsson
// SPDX-License-Identifier: BSD-2-Clause
...

========== file03.c ==========
// Copyright (c) 2008 The NetBSD Foundation, Inc.
// SPDX-License-Identifier: BSD-2-Clause-NetBSD
...

========== file04.c ==========
// Copyright (c) 1992-2012 The FreeBSD Project
// SPDX-License-Identifier: BSD-2-Clause-FreeBSD
...

========== file05.c ==========
// Copyright (c) 2008 The NetBSD Foundation, Inc.
// Copyright (c) 1992-2012 The FreeBSD Project
// Copyright (c) 2017 Jon Severinsson
// SPDX-License-Identifier: BSD-2-Clause-NetBSD AND BSD-2-Clause-FreeBSD
...

==== LICENSE.BSD-2-Clause ====
Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

= LICENSE.BSD-2-Clause-NetBSD =
Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

= LICENSE.BSD-2-Clause-FreeBSD =
Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE FREEBSD PROJECT ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FREEBSD PROJECT OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

The views and conclusions contained in the software and documentation are those of the authors and should not be interpreted as representing official policies, either expressed or implied, of the FreeBSD Project.