I'm not sure why duplicates were ever considered an issue. For certain subjects (like JS) things evolved so quickly during the height of SO that even a year old answer was outdated.
That and search engines seemed to promote more recent content.. so an old answer sank under the ocean of blog spam
But the answer has not become incorrect. It is still correct for that question in that specific context. More likely, the 'canonicalization process' was overly coarse (for SEO?), inconsistent and confused.