Did a quick research for you, and here it is the answer (sorry):
Question:
Is there a time limit for correcting my earnings record?
Answer:
The Social Security Act defines the basic statute of limitations beyond
which earnings ordinarily may not be corrected: 3 years, 3 months, and 15
days after the close of the taxable year in which wages are paid or SEI is
derived.
However, the Act also defines exceptions to protect Social Security
contributors from unfair treatment because of any delay on the part of the
Social Security Administration in processing earnings.
The exceptions permit us to correct errors after the statute has expired and
include authority for us to confirm records with tax returns filed with the
Internal Revenue Service. These exceptions also allow us to correct errors
due to employee omissions from processed employer reports or missing reports.
We are also able to correct errors "on the face of the record," that is,
errors we can find by examining our records of processed reports; and
include wages reported by an employer as paid to an individual but not shown
in our records.
March 24, 2009