The service interval counts whatever you have the odometer set up to read. I have the odometer set in kms, and mine shows 20.000km when i reset it. It drops in 100kms increments. After around 2000kms, mine shows 17400 cause i drive it kinda hard (either stop start city traffic, or max speed highway trips all the way down to the sea side).
If more than a year has passed since your last service reset (But you haven't done more than 20.000kms) it will display the number of days overdue. If you pass the mileage mark before the year passes, it will show you how many hundreds of kilometers you're over the limit.