A certain amount of "Download Credits" will be given to you depending on which plan you are subscribed to.
These credits will be used for every book that was fulfilled successfully before you are charged the plan's download fees. Any unused credits will roll over to the next month.
(See: EditionGuard's Pricing Page)
Please note that if you downgraded/upgrade your plan. all the unused credits from the previous plan will be rolled over to your new plan.