Thanks!  To answer your question:  the historically strong 1982-83 El Nino was followed by Neutral conditions the following winter (1983-84).  It cooled, but not enough to reach the thresholds NOAA CPC maintains for a full episode (5 consecutive 3mo. overlapping seasons < -0.5C).  So it is certainly possible to not have a full blown La Nina after a strong El Nino.  One limitation here is how short the historical record is... we simply don't have a large sample of strong ENSO events, so there is enough uncertainty that we can't rule out anything.  The theories are just that, theories.  While the best ones also have model and observational support, no one theory explains it all which is why forecasting will remain challenging.  We still have to see what plays out.... the 40% chance of La Nina (current odds) is considerably greater than 0%.