This is all very interesting!
> All I have to do is find a list of identified El Niño and La Niña events prior to 1950.
The best I can instantly do is [this page](http://www.cpc.ncep.noaa.gov/data/indices/), which provides the Southern Oscillation Index (SOI) since 1882. I doubt the Niño 3.4 goes back before 1950, since it involves measuring the temperature of a large patch of water in the Pacific Ocean. But the SOI is also a good El Niño diagnostic.