And it's a glitch that the 'average' person will probably never somehow trigger in their life. The amount of overlap required to trigger this issue is such an edge case. Apparently Fidelity's systems went wild after realizing the same person had both a TIN and a SSN and multiple overlapping accounts somewhere.

> Since her account was originally opened with a tax identification number (she was a permanent resident at the time), a system glitch emerged when she recently opened a custodial Roth I.R.A. for her daughter using her own Social Security number. Even though she said she had used her Social Security number at Fidelity for years, it appears her profile and accounts hadn’t been properly merged and updated. A work profile set up by a former employer more than a decade ago with her Social Security number may also have complicated matters. (She said she had never activated or used it.)