As for the 100 shipments, these are counted per month?

As for the 100 shipments, these are counted per month, regardless of whether you use them all or use less, it is not A cumulative

Are you referring to the 100 submissions limit for the FREE plan?

Please note that the limits reset on the first day of each month. To know your current usage and limits of your account, please refer to this guide: Understanding-Your-Account-Usage-and-Limits

You can also check the limits of each plan on our pricing page: https://www.jotform.com/pricing/

Let us know if you are referring to something else.