The SSA retrospective The Story of the Social Security Number traces the changes in Social Security card evidence requirements from 1936–2008, and has a table of legislated and regulatory requirements for using Social Security numbers (SSNs) from 1943–2008.
These tables provide clues as to what other records may have been created about an individual that might contain an SSN. If you have any of those records, matching the SSN will give you some confidence that the records belong to the same individual. However, there are some things to consider:
- Cases exist where duplicate SSNs were assigned (see the linked article for details).
- Many records from organizations which may have asked for SSNs hold those records in confidence, and privacy concerns may bar public access.
- Even when records are accessible, they may not be retrievable by the SSN.
The article is also available for download as a PDF.
I don't know if any of the records referred to in this article are open to the public, but it might be a starting point for further research.
Is the SSN used in public military records?
The SSN appears in Ancestry's database U.S., Department of Veterans Affairs BIRLS Death File, 1850-2010 / fold3's Veterans Affairs BIRLS Death File. The NIH's US Library of Medicine has a fact sheet that describes how the BIRLS Death file is updated.
In my own research, I match the SSN from the following databases and records whenever possible:
Note that not all Social Security Numbers were applied for with an SS-5 form. See "A Taxing Form" posted on 8 Dec 2014 by Judy Russell, on her blog The Legal Genealogist.
The blog post Anatomy of a Social Security Number has information about what geographical clues might be found in the SSN itself (and the periods for which this is the case). It also lists several of the beneficiary codes (letter codes) that may appear on documents when SSNs are used as claim numbers for Social Security or Medicare Benefits.
The Social Security number followed by one of these codes is often
referred to as a claim number. The SSA assigns these codes once
someone applies for benefits. These letter codes may appear on
correspondence from Social Security or on a Medicare card. They will
never appear on a Social Security card.
Two more recent blog posts (July 2015) from The Legal Genealogist:
- Getting that SSN has an update on the requirements for ordering an SS-5, plus some notes on the new database U.S., Social Security Applications and Claims Index, 1936-2007 recently added on Ancestry.com, which is derived from the SSA's NUMIDENT files (see update below).
- a followup to that post, More SSN info, includes a pointer (courtesy of blogger Israel Pickholtz) to the SSN's document, Meaning of a Social Security Number, which is the official version of the information found in the Anatomy of a Social Security Number blog post linked to earlier in this answer. But note too that Chad R. Milliner at Ancestry.com alerted Russell to the notice that the Social Security Administration has begun randomizing SSNs, so that as of 25 June 2011, you can no longer use the first three digits to predict the residence at the time of the application or issuance of the Social Security Number.
In November of 2016, the US National Archives added to its Access to Archival Databases (AAD) website a related group of records from the Social Security Administration, the NUMIDENT files. A PDF on the content and scope of these digital records can be downloaded here: Freqently Asked Questions: Series: Numerical Identification (NUMIDENT) Files, 1936 – 2007 Record Group 47. Section II.4 of this document addresses the differences between the data in the SSDI and this database.
If you have the SSN of a deceased person, you can now search AAD for free to find out other information about how that person communicated with the Social Security Administration. You don't need a subscription, as you would to search Ancestry's U.S., Social Security Applications and Claims Index, 1936-2007. See Ancestry's About U.S., Social Security Applications and Claims Index, 1936-2007 underneath the search box on the previously-linked page for their explanation of what information might be found in this database.
One example from my research: my husband's grandmother's record on NARA's AAD extracts from the NUMIDENT has a value in a field marked "Other Number". A search of my files showed that the number is her husband's SSN. This associates the two numbers, showing me that I'm likely to have the right couple (and not two individuals who happen to have similar names). It also means I have another way to find her entries in the database -- which is important, since her surname is misspelled in both the SSDI and NUMIDENT files.
UPDATE: Having spouses' records linked via the "Other Number" is not very common. NARA's FAQ says, in part:
For 71% of the records, the Other Number field contains the same value as the Social Security Number field. And 13% of the records are blank or have a null value for this field.
(One drawback of the NUMIDENT extracts at AAD is that NARA redacted the content of the death Certificate number file. If they had included that data, I could have matched it against the state's death index, which does include that information.)