Over thme, Congress enacts amendments to Copyright Law. The present Copyright Law includes provisions and revisions passed by Congress through 2009.
THe Law is available both in printed and online form, Circular 92.
http://www.copyright.gov/title17/circ92.pdf

Satellite transmissions are among the recent additions, and several bills with amendments and additions have been put forward in either the House or Senate this year (2010) but have not yet been passed (they may die if support is not obtained in Committee).

The basic Law on which subsequent amendments have been made was enacted in 1976.
Subsequent amendments and additions were made in 1978, 1980, 1982, 1984, 1984, 1988, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998 (the extensions called the Sonny Bono Copyright Extension Act, and the Millenium Copyright Act), 1999, 2000, 2002, 2004, 2005, 2007, 2008; supplementary provisions also were made (mostly covered in the Appendices).

I have not checked which amendments includes the provisions about performers; I suspect several apply.

It is necessary to have the latest version in order to be correct in application of copyright law.