Is he saying that the papers/experiments of Sperry (for which he won the Nobel Prize) were not reproducible? They only tested two new patients. How rare are split-brain patients? (I assume very rare indeed if they could only find two subjects).
I imagine the neurosurgeons doing it to reduce epilepsy also want to preserve as much connectivity as possible, so total severance of the tissue between the hemispheres may be rarer in present population of splitbrain patients as their technique improved?