Social Security Administration has announced that it will accept other proofs of death for its purposes, since it may take some time for many to receive actual death certificates.
Here is an excerpt from a recent SSA eNews:
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RESPONSE TO THE TERRORIST ATTACKS
Social Security has activated special emergency handling procedures for
Survivors claims resulting from the terrorist plane crashes at the World
Trade Center, the Pentagon, and in Pennsylvania on September 11, 2001. The
agency's disaster/emergency procedures allow for alternative proofs of death
in Survivors claims. In some cases it will take months to receive a death
certificate. The proofs of death we will accept include airplane manifests,
lists of employees furnished by employers, and other statements placing a
worker at the scene of the tragedy. For more information on Social
Security's response to last week's events, see our news release.
http://www.ssa.gov/pressoffice/releaseattack.htm
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I hope this helps.