all along vs apropos

all along

adv
  • For the entire time; always. 

prep
  • Used other than figuratively or idiomatically: see all, along. 

apropos

adv
  • To the purpose; appropriately. 

  • By the way. 

  • Timely; at a good time. 

prep
  • Regarding or concerning. 

adj
  • Of an appropriate or pertinent nature. 

  • by the way, incidental 

How often have the words all along and apropos occurred in a corpus of books? (source: Google Ngram Viewer )