\NewBibliographyString{noauthor}
\NewBibliographyString{noeditor}
\NewBibliographyString{nodate}
\NewBibliographyString{notitle}
\NewBibliographyString{nolocation}
\NewBibliographyString{nopublisher}
\DefineBibliographyStrings{english}{%
  noauthor      =   {s\adddot a\adddot},
  noeditor      =   {s\adddot ed\adddot},
  nodate        =   {s\adddot a\adddot},
  notitle       =   {s\adddot t\adddot},
  nolocation    =   {s\adddot l\adddot},
  nopublisher   =   {s\adddot ed\adddot},
}
\newcommand*\nosomethings{noauthor,noeditor,nodate,notitle,nolocation,nopublisher}
\@for \xx:=\nosomethings \do {%
  \expandafter\ifcsname\xx\endcsname\relax\else
  \expandafter\expandafter\expandafter\expandafter\edef\csname\xx\endcsname{\noexpand\bibstring{\xx}}%
  \fi}