Your 1099-R does not have a starting date. You would need to get that from the plan administrator, if you do not have it in your own paperwork from the start.
No Supplemental is different.
Supplemental Security Income (SSI) is a Federal income supplement program funded by general tax revenues (not Social Security taxes):
It is designed to help aged, blind, and disabled people, who have little or no income; and
It provides cash to meet basic needs for food, clothing, and shelter.