From Defense.gov:
The 2009 War Supplemental Appropriations Act established Retroactive Stop Loss Special Pay (RSLSP), providing $500 for each month/partial month served in stop loss status. Service members, veterans, and beneficiaries of servicemembers whose service was involuntarily extended under Stop Loss between Sept. 11, 2001 and Sept. 30, 2009 are eligible for RSLSP.
To receive this benefit, those who served under stop loss must submit a claim for the special pay. Throughout the year, the services have been reaching out to servicemembers, veterans and their families through direct mail, veteran service organizations, and the media. But there is still money left to be claimed, and the deadline is approaching. The average benefit is $3,700.
Individuals who meet eligibility criteria should submit an application by October 21, 2012. By law, there is no authorization to make payments on claims that are submitted after the deadline.