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This article in Smithsonian Magazine presents a brief overview of copyright restrictions in the US and the anticipation of discovering long-hidden gems.
Works in the public domain may be used, re-used, remixed, and built upon without permission. On January 1, 2019, works published in 1923 entered the public domain. Beginning this year going forward in the US, another year's worth of creative works and publications will enter the public domain annually.