Using Google Books Ngram Viewer for legal research?

Well, at least fun to play with Google Books Ngram Viewer. This freely available tool works as follows: “When you enter phrases into the Google Books Ngram Viewer, it displays a graph showing how those phrases have occurred in a corpus of books over the selected years” (of course, normalised per all books of this year). So, now a couple of examples somehow related to what (legal) scholars may be interested in:

(1) blue: "rights"; red: "duties"

(2) blue: "German law"; red: "French law"; green: "Chinese law"; yellow: "Indian law"

(3) blue: "corporate social responsibility"; red: "shareholder value"

(4) blue: "humanities"; red: "social sciences"; green: "natural sciences"

Limitations: what books are we exactly talking about? Is the word really mentioned in a meaningful way? Or were there alternative words in previous times? Thus, more generally, do these graphs show that concepts or the use of language or both have changed? And why did any of this happen? Thus, perhaps, the best way to think about these graphs is that they can show that something interesting is going on, leading to further research in particular topics.