When purchasing additional licenses to an existing TSR account, the licenses will be included in the existing subscription, which will keep the same renewal date.
The following discounts apply:

9-12 months until renewal: 0% discount.
6-9 months until renewal: 25% discount.
3-6 months until renewal: 50% discount.
0-3 months until renewal: 75% discount.

These discounts are additional to the quantity discount specified on the TSR price list.