Comment by inteoryx

I had a similar intuition and graphed unique words per year while writing this. I found, surprisingly, that actually the reverse was true. Unique words per year go up, even as diversity goes down. Another finding that may explain this is that the articles get longer as time goes on - so a simple unique word count may just increase as a function of the authors using more words. There is a period in the late 80's to early 90's where average word counts per article nearly double. I'd speculate that this is about the time The Crimson switched to using computers or good word processing or something that made writing articles easier.

A graph that may get to the heart of your question is something like "Unique word percentage over time" or maybe "What percentage of articles use unique words".