I don't know, this article is explicitly about the problem of trying to link to something you find valuable but its supposedly durable url has been taken offline.

The DOI is supposed to ensure a copy can be found, if it fails to do that in 30% of the cases it's not a very useful, regardless of if a copy exists somewhere online.

I will say that DOI.org isn't the only dDOI resolver and that sci-hub in many ways behaves like one.

One of the few useful cases for IPFS tied to DOI.

ipfs can be inaccessible due ipfs bridges blocking the request.

You can programmatically cycle through bridges, or connect directly to IPFS nodes. Importantly, it’s content addressable; as long as you have a hash, you can find it somewhere (assuming sufficient object coverage).

while of course you should only do this if you are in a country where it is legal, you can look up a doi in libstc.cc, sci-hub.ru, or annas-archive.org

Are there jurisdictions where merely accessing this content is punishable by law?

EDIT: genuinely asking, I know very little about IP law.

there are jurisdictions where making a copy of it is, even for personal use, but others where it is not

I assume viewing a PDF in browser is generally safe everywhere as long as you aren't downloading to HD or cloud? Or is even this activity realistically dangerous without a VPN in some places?

"Viewing something in the browser" is technically downloading. Law system is too archaic to understand how internet works.

this can vary by jurisdiction

i don't think it's dangerous (even torrenting it isn't dangerous) but i don't want to recommend doing something illegal even though it's totally safe

You don't think this alarm should be raised because there exists illegal copies?

Otherwise what is the limitation? What is the failing that makes it not that useful of a study?

Indeed, "we can't find many books if we ignore the libraries!"

More like "we can't find many publicly-available books if we ignore home libraries". It seems prudent to wonder where so many previously-publicly-available books have gone.

both of the mentioned libraries are publicly awailable, seems prudent to count them

The libraries that can be shut down by legal fiat? Hmm.

so any library?