As pointed out, more than one copyright extension has occurred. But it's more than just that: the copyrights are now automatic, and don't depend on something being labeled appropriately, as was true in the USA until 1978. That alone makes "public domain" a much less useful concept, as one is never quite sure what the status of something is upon inspection.
The term of copyright has not just gotten longer, it's gotten less determinate: author's life + some number of years. Instead of a simple date calculation, we have to go reference mortality data, too.
Those two things are a pretty massive change, making it difficult to tell if obscure works have entered the public domain or not.
The term of copyright has not just gotten longer, it's gotten less determinate: author's life + some number of years. Instead of a simple date calculation, we have to go reference mortality data, too.
Those two things are a pretty massive change, making it difficult to tell if obscure works have entered the public domain or not.