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I was reading around the topic of the precise details of subscriber-content licensing on SE, and I found (and read more carefully than the previous times I'd seen it) this thread on FOSS.SE from 2017, which points out that content on Stack Exchange is actually dual-licensed.

The current Terms of Service, immediately after requiring users to agree to license their content under CC BY-SA, go on to require that

you grant Stack Overflow the perpetual and irrevocable right and license to access, use, process, copy, distribute, export, display and to commercially exploit such Subscriber Content [...] as reasonably necessary,

i.e., the ToS explicitly carves out a second license allowing SE to distribute the subscriber content even if their Creative Commons license expires. This can happen e.g. if the subscriber content was provided under CC BY-SA 3.0 and SE breaks the terms of the license, such as by distributing content under a license that's incompatible with CC BY-SA 3.0, such as the 4.0 version of the license. In this sense, it's useful that SE can continue to distribute the content, but the illegal change diminished the protections to the content instead of increasing them: while SE can distribute content, users cannot redistribute it, since the CC BY-SA 3.0 license that SE originally held to distribute it has been automatically revoked.

However: this does not seem to be the case for content contributed before 1 May 2018, as pointed out in the FOSS.SE thread linked above: in the Terms of Service active until May 2018, the equivalent section reads

You grant Stack Exchange the perpetual and irrevocable right and license to use, copy, cache, publish, display, distribute, modify, create derivative works and store such Subscriber Content and, except as otherwise set forth herein, to allow others to do so in any medium now known or hereinafter developed (“Content License”) in order to provide the Services, even if such Subscriber Content has been contributed and subsequently removed by You.

What is the precise status of this clause?

  • Does it permit Stack Exchange to allow others to distribute and modify the content outside of the boxes drawn up by the Creative Commons Attribution-ShareAlike license?
  • Or is this simply an (ultimately unnecessary) precision on the details of what the preceding sentence, which specifies the CC BY-SA license, entails?

Can we ask a Stack Overflow member to clarify once and for all what is the status of this language? Do the Terms of Service specify a dual license to the content? If so, what are the limits to the secondary license, and how do they extend to third parties? Or does Stack Overflow see its rights to the content as specified only by the relevant Creative Commons license?

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