I'm using ENSO dataset from the NIST Statistical Reference Datasets as a test for nonlinear regression code. The data are monthly averaged atmospheric pressure differences between Easter Island and Darwin, called Southern Oscillation Index (SOI). In the test, the data are fitted with three sine cycles (like this).

I got curious about the Southern Oscillations and I started looking for more SOI data. I learned that there are a few different methods of how to calculate the SOI, but none of the other sources that I found (e.g. here) gives the same numbers are in the NIST StRD.

There is a reference in the dataset, Numerical Methods and Software by Kahaner, Moler and Nash, where I found only that the data are for years 1962-1975. So my question is not really about statistics: how the ENSO dataset is related to the SOI data from other sources.