Thanks Bill. I should have noted that the Form 8955-SSA instructions do say in the Who Must File section:
"Plan administrators of plans subject to the vesting standards of section 203 of ERISA must file Form 8955-SSA."
That section ends with the comment:
"Sponsors and administrators of government, church, and other plans that are not subject to the vesting standards of section 203 of ERISA (including plans that cover only owners and their spouses or cover only partners and their spouses) may elect to file Form 8955-SSA voluntarily. See the instructions for Part I, line A."
The instructions for Part I, line start with:
"Line A. Check this box if you are electing to file this form voluntarily."
To rephrase the question, has anyone who is not required to file a Form 8955-SSA ever voluntarily filed one?