Hello and thank you for entrusting me to answer your question.
The reason why you have had trouble finding a clear-cut answer to this question is because the answer depends entirely upon the wording of the particular employment contract, and if no employment contract exists, upon the common understanding between employer and employee.
It may sound obvious, but a commission is entitled whenever an employee has completed all acts that contractually entitle her to the commission
Absent an agreement to the contrary, a commission is generally regarded as "earned" when an employee has completed all actions reasonably necessary to secure the commission. So, absent an employment contract stating to the contrary or a common understanding between employer and employee, this default understanding would likely govern commission entitlement.
Certain equitable principals, such as "unconscionability" can also serve to limit an employer's' ability to restrict commission entitlements. For example, see American Software Inc. v. Ali here: http://law.justia.com/cases/california/caapp4th/46/1386.html
So to summarize, there is no definitive answer to this question because it is a matter of contract. Whatever the contract requires for commissions to be paid will govern, and if there is no contract or clear employment policy governing this issue, then commissions will generally be considered "earned" when an employee has completed all actions reasonably necessary to secure the commission.
I sincerely hope that this information helps you and I wish you the best.
My absolute greatest concern
is that you are satisfied with the answer I provide, so please do not hesitate to contact me with follow-up questions. Also, please bear in mind that none of the above constitutes legal advice nor is any attorney client relationship created between us.