Note that there are thresholds involved in defining the events. There is a third state of neutral temperature deviation as part of the cycle in between events.

Note that there are thresholds involved in defining the events. There is a third state of neutral temperature deviation as part of the cycle in between events. So, you don't just divide the cycle time in half and call it either La Nina or El Nino. Another aspect made clear from the presentation is the different global measurement zones that contribute to the analysis. The actual events aren't as simple as one scalar number, but distribute energy differently around the ocean, and have different localized impacts from this distribution. I suspect that this colors the narrative around particular events depending on who is reporting. But, I agree the chart in that presentation doesn't make the duration of the most recent La Nina seem that unusual in this limited time period. It would be interesting to see the same chart extended back to 1900 or so, but I imagine they may not have a comparable enough dataset.