It is 10% of the gross revenue or what ever % commission was agreed upon in writing.
That means if the tenant renews you owe and if you do not pay and he/she finds out, he/she may bring about legal action for the balance owed on all renewal years.
Typically the agent enters renewal years commission on the listing agreement for the residual commission you owe as a landlord. If the agent obtained a good tenant who stayed there on a long term, he/she deserves the commission from the renewal years.
I have read a case where a agent did not enter a commission clause in the listing agreement covering renewal years. The agent discovered that the landlord renewed the lease on the property with the tenant and did not pay the renewal commission. Legal action was brought on by the agent against hi client/Land Lord and the court ruled in favor of the agent. The court's rationale was that it was implied or assumed that 10% of the commission applied to the gross revenue generated by the tenant not by the initial lease term.
I hope this answers your question.