How is an IPUMS-CPS record uniquely identified?

#1

How is an IPUMS-CPS record uniquely identified?

How does IPUMS CPS variable SERIAL behave across years and downloads?
#2

Two variables constitute a unique identifier for each household record in the IPUMS-CPS: YEAR and SERIAL(year and household serial number).

Three variables constitute a unique identifier for each person record in the IPUMS-CPS: YEAR, SERIAL, and PERNUM (year, household serial number, and person serial number).