Whoops -- accidentally just sent this to Till, re-sending to the full list:
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Hi Till, please see my thoughts inline below:
On Tue, Feb 21, 2023 at 2:19 PM Till Jaeger via lists.spdx.org <jaeger=jbb.de@...> wrote:
[SDW] From a quick search on the Internet Archive, that URL appears to have been the correct URL for that version of the website text at one point in time (at least as of July 2014: http://web.archive.org/web/20140704074106/http://www.unicode.org/copyright.html).
The purpose of the "other URLs" section of each license is _not_ to be a now-current source for that license text, but rather to include URLs which may have been a source for it in the past (as they may be useful for scanning tools, human review, etc. when finding URLs embedded in source code). We don't remove inactive or no-longer-valid URLs because they may remain useful for identification purposes -- see https://github.com/spdx/license-list-XML/blob/main/DOCS/license-fields.md (section C) for one place where this is mentioned.
[SDW] This could perhaps be added to the "Notes" for the Unicode-TOU license, but I'm a little hesitant to do so. For the reasons mentioned above, any of the "other URLs" for any license on the SPDX license list may be incorrect, and I don't think we go through to regularly re-confirm that any of them match the present text.
Follow-up issue: Unicode files refer to
[SDW] I think this is a recurring issue when license stewards reuse old URLs to change the text of a license. https://www.gnu.org/licenses/gpl.html used to point to GPL-2.0 (see http://web.archive.org/web/20030207060604/https://www.gnu.org/licenses/gpl.html) until it later pointed to GPL-3.0 (see http://web.archive.org/web/20100210183622/https://www.gnu.org/licenses/gpl.html). That URL can show up in source code with the author's intent of it having referred to either version. No matter how we handle URLs on the SPDX License List, URLs at most _may_ be helpful for identifying a license, but frequently aren't going to be solely reliable in plenty of cases.
[SDW] The "other URLs" link currently listed there -- http://www.unicode.org/copyright.html -- appear to have previously been a source for finding the Unicode-DFS-2016 license text. http://www.unicode.org/copyright.html as of August 2016 (http://web.archive.org/web/20160823201924/http://www.unicode.org/copyright.html) appears to have had Unicode-DFS-2016 as the license text in Exhibit 1 on that page.
[SDW] From a quick look, that does appear to be a valid URL containing the text for Unicode-DFS-2016 (though I haven't checked carefully to confirm it's a match). Assuming it is, I agree that https://www.unicode.org/license.txt could be added as an additional "other URL" for it.