However, I can provide general information. The onset date (the date the disability began) and pay date (how far back Social Security can pay benefits) can be two different things.

SSA can only pay DIB (aka SSDI) benefits 12 months prior to the date of application. There are some limited exceptions, such as if a prior claim is reopened (then it might be a maximum of 12 month prior to the previous application).

The onset date is just how far back Social Security found the individual disabled. Now, SSA is not going to pay disability benefits BEFORE the onset date. However, if the onset date is more than 12 months prior to the protected filing date (when SSA is first contacted to start an application), SSA will only pay a maximum of 12 months of back benefits. Things get a bit more complicated when the 5 month waiting period is considered, which I have written about here: http://www.socialsecurityinsider.com/2009/04/what-is-the-5-month-waiting-period-in-disability-insurance-cases/

So, why would an individual claim an onset more than 12 months before the protected filing date? A couple of possible reasons: 1) to actually get 12 months of back benefits, instead of 7 (after the 5 month waiting period is considered). 2) to prove disability before the Date Last Insured (DLI) discussed here: http://www.socialsecurityinsider.com/2008/08/date-last-insured/

There may be additional reasons, but that is what I can think of off the top of my head.

As far as the Medicare issue: the general rule on when Medicare begins is discussed here: http://www.socialsecurityinsider.com/2009/06/i-won-my-disability-case-now-i-have-to-wait-for-medicare/

Congrats on the win Micki!