Lap Distance Difference: Route Guide vs Meetup Creation?

I’m in the process of creating a meet up, and noticed that the lap distance shown for a route is different to that shown in any of the route guides. For example, looking at Innsbruckring, route guides show 8.8km with 0.2km lead-in, whilst creating a meet up shows 9.8km. Any idea why there is a difference?
I’m looking to create a meet-up with multiple laps with a banner finish, hence wanting to know the accurate number.