Apologies then, honestly thought you were on the wind up.
No, it's 17 'Open' spots which anyone can fill.
There's 4 'Club Trained' spots which can only be filled with players who have been at the club for 3 full seasons(?) before the age of 21.
And there's 4 'Association Trained' spots which can only be filled with players who have been at any other club in the association for 3 full seasons(?) before the age of 21.
Hence, Gael Clichy was French but was 'Club Trained for Arsenal but 'Association Trained' for us.
Nationality doesn't come into it at all.
Hargreaves was English but always took up an 'Open' spot because he moved to Germany when he was young.