Long term disability insurance plans are frequently governed by federal ERISA law. In ERISA long term disability plans, typically there are Plan Documents, in depth legal documents actually creating the plan, and a Summary Plan Description, more understandable summaries of the plan documents usually given to the employees.
For a while, if the Summary Plan Description differed from the actual Plan Document, the Summary Plan Description could be used as the legally binding document. After all, the Summary Plan Description is more accessible and understandable to most employees. Also, the Summary Plan Description is the document that is usually given to employees.