Field help (PLFSTRDAT) 

If the plan code already exists in the Budget guideline function (GESBUR), the Start date and End date fields are automatically populated with the dates entered in the reference budget. You cannot modify these dates.

If you create a new plan code without linking it to a reference budget, you can enter any date.

When a plan is final, the plan code, the start date and the end date automatically populate the training requests.