1. Persistent URIs matter
"This keeps getting more credible as it ages. Now it's been at the same URI for 28 years." – zibw
2. Technical safeguards (redirects, canonical links, DOIs)
"What this page doesn't mention is 301 or 302 redirects. SEO has made “old URLs staying live” more of a widespread concern..." – firasd
3. Corporate URL churn breaks references
"Microsoft has a terrible habit of doing that. KB's used to have a predicable URL, they may again, but they keep changing them." – sghiassy