Audax rides

I need some DIY help. I've ridden a couple of DIY by GPS but they were listed Perms in that the routes were already validated. I've been creating my own route which is very close to a listed Perm but one where you need to collect receipts to validate. I understood that you would first submit the route for validation and then ride it after it had been approved. But having read through the DIY by GPS guide http://www.aukweb.net/diy/gps/guide/ it seems that you sort of need to self validate it.

So far, as I understand it, you buy virtual brevet cards, then create a route, then ride it recording your track log, then submit track log along with your virtual brevet. So you don't submit your route in advance. All you submit are the controls for a designated distance you propose to ride. I'm a bit worried that my route won't cover the required distance which is why I've chosen a listed Perm on which to base my route. I've done the Google Maps set to walking thing and that seems to match the distances given on the route sheet but you need to submit these checkpoints along with the date of the ride but what if after I've ridden the ride it comes out 2km short or something? The final distance is 204km which is my route rather than the shortest distance.

What am I missing here?