I have no idea whether there is a sub-genre within the history of economic thought that looks at the evolution of Readings supplements over the years. Teachers of economics (especially intro) get these in the mail all the time, but find ways to part with them as they clean office shelves every few years. I have held on to the earliest one I ever found, Arleigh Hess, et al. Outside Readings in Economics (1951).
The latest in my small collection is Craig Newmark's Readings in Applied Microeconomics: The power of the market, which I am thoroughly enjoying.
What changes over the years? Obviously, the questions that engage economists as well as the tools and approaches that they use.
There are many ways to track these changes. But following the evolution of the Readings collections involves a market test: Which selections are thought by editors and publishers to matter most to those who want to fashion the best possible introduction to economic thinking?
And, in my view, it is much better to teach or learn the stuff in 2009 than in 1951.