Don't quote me on this if I'm wrong but I'm sure the squad numbers that have been released isn't a definitive list of those currently at the club that can be expect to be in and around the first team this season. Obviously as new players are signed they will be given new numbers so I'm sure there's nothing stopping some of the younger players like Shaw and Hoskins being given a number if they start to impress in the U21's.
No your right anyone can still play but it would be much more likely for a player with a number to play solely because it tends to mean these are the main players the Manager is planning to use for the coming season.
