Hi Grace,
Thanks for reaching out to the Adobe Stock community.
With the three-asset/month plan, the 10-asset/month plan, and the 40-asset/month plan, your unused licenses roll over to the next month as long as your subscription is active. The rollover limit is 12 times your subscription entitlement; for example, a maximum of 120 assets roll over for the 10-asset/month plan.
For more information, you may also refer to Common Questions about plans, purchasing, and availability, Adobe Stock
Feel free to update this thread in case of any additional questions.
Regards,
Twarita