When charts [don't quite] speak for themselves: Supreme Court Politics

More or Less Numbers posted the following interesting chart on "Supreme Court Politics"**.  The blog ends with the note that "the graph speaks for itself" and while the graph is informative and raises a number of interesting questions, it doesn't actually answer those questions, and thus doesn't really "speak for itself".  Notably:

1. After the initial rise in number of abortions in the wake of Roe v. Wade, the number of abortions is fairly flat, with the exception of two enormous dropoffs in 1997-1998 and 2012-2013.  How does one explain this pattern?  I /think/ this is because of legislated increased access to birth control, but am not sure.  This is a vital followup question to understanding this chart.
2. Are the absolute numbers from 1974 and 2014 are directly comparable?  I doubt it.  I'd like to see this chart with the y-axis showing the number of abortions relative to the number of women of childbearing age, the number of pregnancies, etc. to arrive at more comparable abortion rates across the years.
3. Where do the numbers prior to Roe v. Wade come from?  In the absence of legal abortions, I seriously doubt the validity of abortion numbers from 1970-1972.   It would be great to see more discussion of these numbers.

** via R-Bloggers, via Feedly