When all else fails, look up the instructions https://www.irs.gov/pub/irs-pdf/i109495c.pdf See page 12
2A. Employee not employed during the month. Enter code 2A if the employee was not employed on any day of the calendar month. Do not use code 2A for a month if the individual was an employee of the ALE Member on any day of the calendar month. Do not use code 2A for the month during which an employee terminates employment with the ALE Member.
2B. Employee not a full-time employee. Enter code 2B if the
employee is not a full-time employee for the month and did not
enroll in minimum essential coverage, if offered for the month.
Enter code 2B also if the employee is a full-time employee for
the month and whose offer of coverage (or coverage if the
employee was enrolled) ended before the last day of the month
solely because the employee terminated employment during the
month (so that the offer of coverage or coverage would have
continued if the employee had not terminated employment
during the month)