With SSDI there is a waiting period of 5 full months, starting the first of the month after the onset of disability, before benefits are paid. Then there is a max of 12 months retro pay. So an onset date of 17 months prior to application would be fully favorable. Since she applied 16 months after her disability date, she will likely get 10 or 11 months of retro pay-depending on the date of her application. Even if she applied 16 months ago, she would not have received any additional benefits due to the waiting period.