Whether it's your current training plan or a past plan, you'll see a start date annotation showing when the plan first began.
This annotation can be dragged and dropped anywhere on Calendar. Therefore, if you started a plan and didn't complete the first ride until a few days later, you can drag the annotation to better align with your workouts.
Along with that, you can click on the plan annotation to open both its description and the option to delete the plan. This can be done with your current, past, or future plans.