by the by vs unlooked for

by the by

adj

  • Incidental; unplanned. 

prep

  • Used to introduce a new topic; incidentally, by the way. 

unlooked for

adj

  • Not expected or anticipated; unforeseen. 

  • Not looked for, not searched for. 

How often have the words by the by and unlooked for occurred in a corpus of books? (source: Google Ngram Viewer )