In which context would the difference in licensing rules between CC BY-SA 3.0 and CC BY-SA 4.0 actually matter?

Question

Quoth Jonathan Reez in this MSE question:

Currently there's a big controversy over SE changing the licensing from CC 3.0 to CC 4.0. Regardless of whether this change was legally solid or not, could someone provide a specific example of how this licensing ambiguity affects our ability to copy, share and reuse content published on SE in the past?

Let's say I find an interesting piece of code on StackOverflow from 2017 and add it to my open source project with attribution, citing CC BY SA. Could the author of this piece of code claim a copyright violation somehow, given the licensing ambiguity? The way I see it - the code is licensed under either 3.0 or 4.0 and the difference between the licenses is so small in practice that knowing the exact version shouldn't matter. Whoever wrote the code couldn't suddenly claim that the licensing change completely revoked their original CC attribution, making it impossible for others to reuse their content.

Note that I'm not interested in whether or not the licensing change was legal/moral/appropriate/cool. I'm merely asking about how it affects my rights to reuse content posted on SE.

I believe users on this site are more qualified to help us in this matter. Could you provide a definitive answer to the question above?

Answer 1

One non-trivial difference is that CC 3.0 is a class of licenses, one per country. If something is licensed under 3.0, does that refer to the US version, the German version, the UK version? Copyright law differs across jurisdictions and US versus German versions could reflect local differences in law.

CC provides a "what's new" document explaining what they think the differences are. For instance:

sui generis database rights are not explicitly covered by the 3.0 unported licenses has led to confusion in jurisdictions that recognize those rights. Version 4.0 removes any doubt, pulling applicable sui generis rights squarely within the scope of the license unless explicitly excluded by the licensor. It also allows database providers to use the CC licenses to explicitly license those rights.

There are various differences between versions (US 3.0 vs. International 4.o, English), for example "collective work" is no longer defined (because the license doesn't refer to "collective work"), likewise "Derivative Work" -- these are terms written into US copyright law, so the earlier US-specific version reflected US law (it now talks about "Adapted Material"). There does not seem to be a huge difference in that which is allowed across versions, but there is a difference (improvement) in comprehensibility.