Postscript:
I’m under the impression he landed in Honolulu. The apparent intention was that his ‘grandparents’ would collect him.
Prior to 1972, aliens weren’t required to have a SSN assigned.
A SSN could be requested that was sent to a mailing address that was not the same as the primary address.
If he flew under the radar as a foreign student, he could have not requested a number until a much later date, even into his twenties. This would coincide with lack of a legit registration for selective service. I believe those males registered with SS at birth get the SSR letter 6 months prior to the 18th birthday.
1972 Legislation authorizes SSA to assign SSNs to all legally admitted noncitizens at entry and to anyone receiving or applying for a federal benefit.
https://www.ssa.gov/policy/docs/ssb/v69n2/v69n2p55.html