Ann: NTCELL Parkinsons trial patient data 2 years after implant, page-55

That's right, they were very confident based on previous work, but ignored warnings from other studies about the strength and duration of the placebo response. And they were looking for a large response to justify the risks and expense of treatment. They also have a problem in that not all patients are capable of a significant response, but they don't know which ones, nor the optimum dose. A further confounding variable is that all patients are on drug treatment and their performance in the tests may vary from day to day because of things like sleep or emotional state...
The intention of the study was to provide evidence of sufficient safety and efficacy that they could apply to the local regulators for permission to conduct a larger commercial trial. To do that they would need this trial to show a statistically significant improvement over the controls. The mood seemed optimistic so it would seem likely that the controls in the final cohort may have caused an upset.