My concern is solely with the legal parameters of copyright, not with the ethical/moral requirements for accurate source citation, and I apologize for any confusion I've created on that point.  Let me be as clear as possible that researchers have a strict obligation to provide citations to the <em>Archive</em> copy of published or unpublished work, whether in or out of copyright.  Such a citation should, indeed, include not only the "place" where the copy was accessed (i.e., the <em>Archive</em>), but also, when applicable, the repository where the physical original resides.  This is little different than the expectations for citing microfilmed copies, though many of today's researchers would be too young to have learned those expectations.