Route distances shorter than stated

Hi, I’m new to Zwift and just wondering why some routes seem to be shorter than the advertised length.

For example, I just did London Classique which was stated to be 5.4km + 5.7km lead-in. However, I got the route badge done in under 6.2km total.

Do lead ins only apply to races or something?

Many thanks,

Guess the lead-in for that event contained most of the circuit.

There’s a lot of info on the interwebz about badge hunting, lots of courses you have to ride for longer than the stated route distance because of lead-ins etc.