iPhone Calendar remembers too much delivery information

I use the calendar app on my iPhone a lot. It is helpful when I create an appointment I had before that the app fills in the details. But it remembers too much. For instance I plan deliveries I get at home. But I have more than one delivery company. And now each time I plan a delivery I see the delivery details as tracking number from the first delivery. If I delete that information it also should be deleted from what calendar remembers.

[Re-Titled by Moderator]

Original Title: Calendar remembers to much