As a near 30 year ear ringer I'm genuinely pleased to hear that you've got silence.
I would absolutely stick to the point I made about the trial criteria though. If the device can be intended for use by any person regardless of how much time they've had tinnitus why not make the eligibility criteria; troublesome tinnitus onset >6 months with no upper time limit?
Aside from anything (although I'd appreciate
@PeterPan's view on this because of his experience with statistics) I'm inclined to believe that focusing on a 6 month window could produce a statistical anomaly.
P.S.
@PeterPan FYI in case you're unaware, eligibility criteria for the current UMich trial of their bi-modal stimulation device states:
Preferably onset of tinnitus less than one year ago, but present for at least 6 months. Tinnitus should be bothersome.