If you like to avoid that your media campaigns are running longer than for one fiscal year you can manage this by checking a setting in the App Launcher → Administration Settings:
If you now want to add a line item which runs into the next year you will get an error message. The system does not check manually entered dates on media campaign level as these get rolled up from the line items anyway.
Remember that this feature is NOT reversible. If you have it turned on, it stays on.