I've certainly looked and not been able to find anything in the rules that specifically covers this, so that's rather frustrating!Other rules are different for the two different categories, so it's not impossible that this one is different too. I can't see any other reason why they would have elevated Schade rather than Cox. You're right that Blicavs was the nominated rookie in 2014, but it wouldn't be the first time that the AFL approved something without realising that it was against their rules.
Carlton named Irishman Ciaran Byrne as their (pre-season) nominated rookie last year. The question is, was Byrne a Cat. B Rookie in 2016, or was it fellow Irishman Ciaran Sheehan (they couldn't both be Cat. B). I had Byrne as Cat. B and Sheehan Cat. A, but that was purely based on the fact that the AFL had them that way in 2015 ( http://s.build001.aflprod.com/staticfile/AFL Tenant/AFL/Files/2015finalclublists2.pdf ):-
http://www.afl.com.au/news/2016-03-16/rookie-watch-who-will-be-promoted-at-your-club
Ciaran Byrne played in two NAB Challenge games and was confirmed as the Blues' nominated rookie on Tuesday as they have 39 primary-listed players.