Question about work status codes

Hi- I’m trying to create a variable that differentiates voluntary (economic reasons) from involuntary (non-economic reasons) part-time workers using information from CPS WKSTAT variable. I’m not sure what these codes mean or how to categorize these workers. Do these codes mean part time or full-time status:

12 Part-time for non-economic reasons, usually full-time

21 Part-time for economic reasons, usually full-time

15 Full-time hours, usually part-time for non-economic reasons

Also, does “not at work” mean respondent is temporarily absent from a job and still employed?