>perl -wMstrict -le
"for ('TAG1 text one TAG2 etc',
      'TAGS text ess TAG2 etc',
      'TAG1 text two TAG2 etc',
   ) {
   print qq{'$_'} if m{ \A .... (?<! TAGS) .* TAG \d }xms;
   }
"
'TAG1 text one TAG2 etc'
'TAG1 text two TAG2 etc'