Hi Carl,
Yes, it is possible for employees to request leave within more than 1 calendar year. They cant however be enrolled in 2 leave plans that accrue the same leave type, at the same time. You would have set an end date for the first plan before starting the second. Employees can be assigned to multiple leave plans at the same time but they cant have the same leave types accruing within more than 1 plan they are assigned to.