I wouldn't read anything in to Addy wearing a 17 shirt.
He was supposed to be number 17 last year, until the whole debacle of removing the number 16 when Winterstein left. When they did the presentation night and the e-mail list of numbers different (some idiot moved everyone up a number in the e-mail, but not on the presentation night).
So although Addy was 16 last year, he was actually supposed to be 17, and was issued with training gear last season with the number 17 on. If you notice, numerous players wore training gear one number out (Adam Henry wore gear with 22 on for example).
The picture in the T&A could just be one of him in last year's training gear, so the fact it has 17 on is irrelevant.
Although now I've gone through all that, he'll likely be given 17 this year too....