What is the notation the author uses for historical prices? The one with the year in lower index and some other number in upper index? I tried <your favourite search engine>ing that but I don't know how it's called.
I've never seen it before, but it appears to be inflation notation. It's a subscript on prices, so the year is the original year of the price, and the cost above it is the inflation-adjusted equivalent in present-day dollars.