The $6,000 exclusion is a:

Special Exclusion. If you (and your spouse if filing jointly) will never be able to receive Social Security or Railroad Retirement benefits because your employer did not participate in either program, you may qualify for the Special Exclusion. If you qualify, you can claim $6,000 (married, filing joint; head of household; qualifying widow(er)) or $3,000 (single; married, filing separate). Note: Do not claim the Special Exclusion if you (or your spouse if filing jointly) will ever be eligible for Social Security or Railroad Retirement benefits.

I also found the wording a little tricky until I saw the reply.  TT should include this response or something like it in the context help of this question.