Variable cpsidp - unique observations

Good evening,

I am working with CPS ASEC data and am looking at two time periods: 1978-1982 and 2015-2019. For each time period, I would like to keep only unique observations (I am interested in the cross-section of both time periods). I am therefore looking at the variable cpsidp, which identifies unique observations. However, this variable does not exist for 1978-1982. How can I now identify unique observations for this time period?

Thank you very much for your answer!

In the early years of the ASEC data, individual ID variables (such as SERIAL and PERNUM) exist but they do not reliably identify the same individual in adjacent samples. For more details on this issue, see the Drew et al. paper on this topic. So, while unique ID variables exist for this time period, they are not reliable for linking observations over time or uniquely identifying individuals in the ASEC prior to 1989.

Thank you very much!!