Your right Young was £9.6m but with add ons, some of which will have already kicked in with his England appearance. The total fee will/could rise to £11m and is very likely to do so. Davies I believe was £8m but none of us know for sure as it was undisclosed thus the fluctuations on here. As for Petrov that is rather more simple, that was £6.5m I thought that was pretty much universally accepted to be honest.
The problem is these days transfer fee's is that they aren't simple as so many aren't disclosed and there are so many add ons.
I don't remember ANY add on for Young, and I thought it was universally accepted that Davies was 10 mill... as for Petrov depending on the poster is 6.5 - 8.5 million. AIRI
Well here you go on Young for a start.
Scroll down a bit