[whitdav1]

On reflection, I think @thegavver is correct. There was an update for the earlier models, which meant that although only one figure is displayed, there are now two countdowns. The one displayed is is the lower of the two - oil service or main service. The oil service reset is dealer only I think. Assuming your car has had the update the latter will apply. Sorry if I caused confusion - I no longer have my MY17 to check.
The bit about average mileage does apply though, hence wild fluctuations are possible if you do a long trip.

You can reset both with Foxwell NT710,

Oil service reset - sets mileage to full reset distance less distance travelled since last full reset or last oil reset if there's more than one Oil reset since the last full reset.

Hope that makes sense - Full reset Distance for an ingenium diesel 2017 is 31000 KM

Foxwell NT710 Bi-directional Scan Tool Upgraded Version of Foxwell NT530 and NT510 Elite