Once an artist goes over the payable threshold, the system will reset and start again for the next statement run. It will only "Carry Over" for as long as the amount is under the minimum payable. It will be up to you then go back and mark as paid and payout to your licensors as you go.
This is to make it easier for clients to avoid paying out twice in case, for example, you forgot to mark a statement as paid and the amount was carried over to the following period.