An incorrect representation of the 1972 cross-section is provided in CDF summary variable VCF0703 (voter registration and turnout). This is the result of standard processing in 1972 when question administration was not, however, standard.

For 1972, VCF0703 data represent all voters but exclude many nonvoters. This is because the question on registration status in the 1972 Pre-election wave systematically excluded approximately half the respondents, while the Post-election turnout question was administered to all respondents.
The standard VCF0703 recode was to code all voters by default to 'voted (registered)', and then to code only non-voters for registration status, however about half of nonvoters were INAP in the 1972 registration question [note: standard procedure recognized that registration questions have typically been administered only to nonvoters, except when administered in the pre-election wave for a handful of pre-post studies before 1978].