Sunderland are making a nice habit of producing and nurturing young players, and selling them for sizeable transfer fees. And although Sunderland have really only done that once, with the sale of Jack Clarke to Ipswich Town, they could’ve done it several times during the summer transfer window just gone. Sunderland have several players in their first-team who attracted transfer interest over the summer, including names like Anthony Patterson, Dan Ballard, and Jobe Bellingham among others, and if any left then it would’ve been for a huge profit. In the end, Clarke sealed an initial £15million m…