U.S. Government Authors Copyright-free

["Alvin Hutchinson" <HUTCHINSONA@si.edu>]

Wiley InterScience journal websites identify when an article is in the
public domain because it has been authored by a U.S. government employee.
The supplemental text accompanying a recently published paper reads, "This
article is a US Government work and, as such, is in the public domain in
the United States of America "
 
I should first say that I am glad to see this recognition by a commercial
publisher and although such a statement is evidently required by by
copyright law, there doesn't seem to be widespread compliance by other
publishers.
 
However, I wonder about restrictions that publishers face when publishing
federally authored works. Namely:
 
If the second or third (or thirteenth) author is a federal employee, is
the article in the public domain?
 
Since no rights have been transferred can the publisher's PDF version
truly be considered 'theirs'?
 
Finally, when a publisher offers single-article sales via their website,
is it unlawful to sell one of these federally-authored papers?
 
I realize that many liblicense subscribers may be reluctant to offer what
would amount to legal advice, but any thoughts on the matter or references
to other material would be greatly appreciated. Please also let me know if
I am missing an important element of this issue.
 
Many thanks in advance,
 
Alvin Hutchinson
Smithsonian Institution Libraries