It seems to me that currently the variable OCC90LY for ASEC samples does not contain codes for unemployed. The code 991 for unemployed is not available for any ASEC sample:
It seems that those unemployed are classified as 999 (Unknown) in OCC90LY. I say that because when I look into another occupation variable, OCC10LY, for the same observations, most are classified as 9920 (Unemployed, with No Work Experience in the Last 5 Years or Earlier or Never Worked).
Why are the unemployed classified as 999 in OCC90LY? is it safe to assume that those 999 in OCC90LY are actually unemployed?