Skoda Superb Flexible Service Interval




Could someone please give me some explanations about the "Flexible Service Interval" of Skoda cars? As far as I understand, it basically means that the maintenance interval (e.g, the amount of km or time travelled) is not fixed but dynamic based on the condition of the car. So, how can I know when the car should be brought to huolto? Take my car for example. The last huolto is with Km-määrä of 73500km (is this the number of km the car has been driven at huolto time?), and the current mileage is 91000km. When is the next huolto?

And btw, what does the "Työmääräysnro" on huolto papers mean?

Thank you!