From the January 1985 Software Documentation Products Directory (EJ-26361-78),
first page:

3. RIGHT TO COPY

   Beginning January 1, 1985, Digital customers are given a right to copy, at
   no charge, any Digital Archival Software Documentation Publication
   (excluding restricted or third party owned) that we no longer offer for
   sale.  However, the copyright is retained as the exclusive property of
   Digital Equipment Corporation.