TN 33 (11-23)
If the agent is an employee, the commissions are earned in the month the beneficiary completes the last act required to entitle them to the commission.
If the agent is self-employed, the commissions are earned in the year in which they are received.
Where allocation to a particular month is material to an employee, and neither the beneficiary nor the employer knows when the last act was done, assume the act was performed in the month the commission was paid.