CPS ASECFLAG before 1976

In the sample selection page I can choose ASEC samples from 1962 on. However, when I examine the data I downloaded, I can seen that ASECFLAG is only defined for years 1976 onwards. I couldn’t find much information in the documentation provided for that variable. Why is ASECFLAG defined only for 1976 onwards?

ASECFLAG indicates whether the respondent is part of the ASEC or March Basic sample, according to the documentation. If you look at the availability of samples, ASEC is available from 1962 onwards (under the ASEC tab), whereas Basic Monthly is available from 1976 onwards (under the Basic Monthly tab). Therefore, prior to 1976, ASECFLAG is unnecessary as all respondents are part of the ASEC.

Thanks for the response. I think that having a consistent ASECFLAG variable is more useful, regardless of whether it is necessary or not. That way researchers can can just subset their data using ASECFLAG == 1 and be sure that are pulling all the ASEC years.