libpng changes over the years

[jlovejoy]

see https://gitlab.com/fedora/legal/fedora-license-data/-/issues/296

http://www.libpng.org/pub/png/src/libpng-LICENSE.txt is the URL for both libpng-2.0 and Libpng

the first part/license:

• is a match to libpng-2.0 (and this is the URL is referenced in the SPDX entry) which was added for version 3.5 in 2019

the second part/license:

• SPDX added https://spdx.org/licenses/Libpng.html in 2010 for version 1.4 of the SPDX License List (see https://lists.spdx.org/g/spdx/message/236?p=%2C%2C%2C20%2C0%2C0%2C0%3A%3Acreated%2C%2Clibpng%2C20%2C2%2C0%2C22079229
• discussion of this at https://lists.spdx.org/g/spdx/topic/22079227#msg235
• SPDX added what existed on that same URL at that point in time. See https://web.archive.org/web/20101202114005/http://www.libpng.org/pub/png/src/libpng-LICENSE.txt

BUT over the years, various things were updated such as the list of names and references to version numbers (which would be replaceable by SPDX matching guidelines, but need markup added)
More substantial text changes occurred as well:

• Feb 2016: pnggroup/libpng@f78d1cd#diff-c693279643b8cd5d248172d9c22cb7cf4ed163a3c98c8a3f69c2717edd3eacb7
• Feb 2016: pnggroup/libpng@08bd765#diff-c693279643b8cd5d248172d9c22cb7cf4ed163a3c98c8a3f69c2717edd3eacb7
• July 2018: pnggroup/libpng@c36c09f

libpng-2.0 was added in Nov 2018, which also altered some of the text order, see pnggroup/libpng@e79085a

question is for SPDX now: should these various changes over the years be handled with markup or constitute a new license?