Your Mom is not eligible for retroactive benefits fom uour Dads SSDI.

Retroactive benefits for months prior to attainment of FRA are not payable to a retired worker, spouse, or widow(er) if this results in a permanent reduction of the monthly benefit amount.

The amount received for early retirement will be reduced.

Did he withdraw his application for early retirement?

Workers planning for their retirement should be aware that retirement benefits depend on age at retirement. If a worker begins receiving benefits before his /her normal (or full) retirement age, the worker will receive a reduced benefit. A worker can choose to retire as early as age 62, but doing so may result in a reduction of as much as 30 percent.

There will be a reduced amount paid for each month before retirement.

If you start receiving benefits early, your benefits are reduced a small percent for each month before your full retirement age.

If for some reason you decide that you started retirement process too early? You can request to withdraw your retirement application Within a certain amount of time it's no penalty. This is only allowed to happen once.

If you change your mind about starting your benefits, you can cancel your application for up to 12 months after you became entitled to retirement benefits. This process is called a withdrawal. You can reapply later.

Social Security - Starting Your Retirement Benefits Early here.

Early or Late Retirement here.

Social Security Handbook 1513 Retroactive Effect of Application here.

Social Security - Starting Your Retirement Benefits Early here.

Retirement or Spouse's Benefits here.

Form SSA-2 - Information You Need to Apply for Spouse's or Divorced Spouse's Benefits here.

Social Security - Starting Your Retirement Benefits Early here.

__ Withdrawing Your Social Security Retirement Application__ here.