I've posted a link to a recent study by Matt Parker at North Carolina State University:
Feel free to read the abstract or the entire article. In general, the study debunks several of the "myths" surrounding veer-back-veer. In particular, the "wrong-orientation of spin" imparted by backing aloft on the updraft has little effect on the efficacy of tornado production. Certain factors that are known to be detrimental to tornado production sometimes, but do not always, accompany veer-back-veer, and he suggests that forecasters focus on those things.
Yet another reminder that certain popular notions in the forecasting community do not necessarily have rigorous scientific evidence that supports them.