Ann: Half Yearly Report and Accounts, page-17

I think you would have to ask. Blinded in this case just means they don't know which patients received sham surgery. However if they have access to raw blinded results they would know the dose that was implanted by looking at the date of surgery. In other words, they might be able to see that the second cohort of patients is doing better overall than the first. The DSMB would have access to the unblinded data, since they need to be able to stop the trial in the event of any adverse events, so they would need to know which patients had what and their progress, but that wouldn't be shared with the company. It may be that they have a scheduled interim analysis based on the still blinded data at say 3 months after implantation. Maybe ask Ken Taylor?