I was just playing around today and found my great-grandma Neill in the Social Security Death Index. She died in 1965 and I never really thought to even look for her in the index. I don't need her SS5 form, it costs $27 and I have no doubts as to who her parents are and all that. However it makes the point that you never know if someone is in an index until you really look. I incorrectly assumed all my farming ancestors from her generation were not in the SSDI.
So, go ahead and look. You never know what you may find. If this had been a brick wall ancestor, getting a copy of her SS5 form from the Social Security Administration might have been helpful. And I NEVER buy the certified copies of records from the link on this site. They are entirely too expensive.