In 1875, the American Express Company established the first private pension plan in the United States.

I can also see a situation where the SSA recipient in 1940 was born in 1875. The recipient age 65 could have married someone very young for 10 years. That younger person could be on survivors benefits and continue receiving payments.

Here is an example: https://www.ssa.gov/history/idapayroll.html

On January 31, 1940, the first monthly retirement check was issued to Ida May Fuller of Ludlow, Vermont, in the amount of $22.54. Miss Fuller, a Legal Secretary, retired in November 1939. She started collecting benefits in January 1940 at age 65 and lived to be 100 years old, dying in 1975.

https://www.ssa.gov/pubs/EN-05-10084.pdf

https://www.ssa.gov/survivor/eligibility

So if in 1965 this retired person married someone age 18... Then that person at 18 never remarried. Could they end up in a situation where they receive survivors benefits from the original applicant?

The recent spouse would be born in 1947 and marry in 1965 for 10 years until their spouse's death... not have remarried or worked, then at age 60 in 2007, derive survivors benefits from original applicant?