Copyrights as extended estate assets

JLM's post below reminded me of something I spotted over the weekend. Back in 1976 (taking effect in 1978) the copyright law was amended to grant longer periods of protection for intellectual property.  Something about the Mickey Mouse copyright approaching its end, as I recall.  From Duke Law, here's a list of items from the 1950s that would have entered the public domain this year, but for that legislative amendment.

For the estates of creative types, copyrights could be the most valuable of estate assets.