Public domain; a search on records yields no results for a "Celebrating 20 Years on PBS", nor any image-based material made by Family Communications Inc. in 1988, nor any registering up to '93. Claim by Everett Collection also yields no results.
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This work is in the public domain because it was published in the United States between 1978 and February 1989, inclusive, without a copyright notice, and its copyright was not subsequently registered with the U.S. Copyright Office within 5 years.
Unless its author has been dead for several years, it is copyrighted in the countries or areas that do not apply the rule of the shorter term for US works, such as Canada (70 pma), Mainland China (50 pma, not Hong Kong or Macau), Germany (70 pma), Mexico (100 pma), Switzerland (70 pma), and other countries with individual treaties. See this page for further explanation.