Yep. AFAIK the IRS does not 'see' "social security accounts numbers" they 'see' "tax ID numbers". My study of the IRS specifications for e-filing or the like revealed lack of any computational distinction between an "EIN" or an "SSN" entered on a form or into a database. Since a year or two such may have changed for some reason or another. The IRS, a bureau of the U.S. Department of the Treasury, does appear to maintain some kind of link between the IRS and SSA for verifying whether an SSAN exists. AFAIK, the IRS and the US Department of the Treasury are wholly separate from the U.S. Social Security Administration. While the digits of the SSAN might generally be the same as that of a US tax ID or account # established with the IRS, they are not at all the same accounts and there is no inherent link between the two accounts. The IRS account would likely never, ever exist if a SS-4, 1040, W2 or W4 was never filed.