I haven't seen that Al. Have you a link to the info?
What I've seen is that the U18s run the Whittle Pike race route which is technically too far for the U16s.
But now that you've kyboshed the trial at Coiners

and they are using Cowpe, it is clear they have to run the U16 & U18 together as the World Youth Challenge is for those at the bottom of the U18 and top of the U16 age groups.
I can't see the need to up the distance though.
The World Youth Challenge is 5.2k/285m for Boys and 3.5K/190m for Girls so I can't see them sending the athletes around 8.2k/488m
Perhaps someone can clarify?