I have the Watchtower Library but only the 2008 edition, so it's not current. I split it up in increments to compare the periods of time. They are in 19-year increments, with the last being 18 because again, I only have up to 2008, but this is what I found:
From 1950 to 1969: The Watchtower mentions "Apostate" 190 times and the word "Apostasy" 87 times. The Awake doesn't mention either word and there were no books or KM's of that time that showed up in the search. So, looking at just the Watchtower and Awake, we have 277 mentions of apostasy in the traceable period prior to 1970.
From 1970 to 1989: The Watchtower mentions "Apostate" 313 times and the word "Apostasy" 292 times. The Awake mentions "Apostate" 30 times, and "Apostasy" 39 times. The books of that period mention both words 149 times combined, and the KM's mention them 7 times combined. This means that apostasy was mentioned 830 times in the period of 1970 to 1989.
From 1990 to 2008 (which is all I have right now): The Watchtower mentions "Apostate" 215 times and the word "Apostasy" 208 times. The Awake mentions "Apostate" 23 times and "Apostasy" 10 times. The books of that period mention both words 138 times combined. The KM is interesting in this time period because, while it mentions "Apostate" 13 times, there is no record of it mentioning "Apostasy" after 1999. From 1990 to 1999, it's mentioned 6 times. So the total here is 613 times apostasy was mentioned between 1999 and 2008.
This shows, to me, that the 70's and into the 80's were a desperate time for the WTBS due to the failure of the 1975 prediction of Armageddon. After the 80's dwindled out, they gave it a little bit of a rest because the danger level wasn't SO high as it was then...
I think, though, that we are going to see more and more mentions in the time to come...particularly because of the internet and the fact that the society is dead-nuts SCARED of apostates speaking out and waking up the sleeping rank and file.