By my understanding, trades/cuts cause the current season's bonus to be applied to the current season's dead cap and any future season(s)'s bonus(es) to be applied to next season's dead cap.
So if you have someone signed through 3 seasons after this one and trade/cut him, 1 season of bonus will count toward this season's dead cap and 3 seasons of bonus will count toward next season's dead cap.
Hence, you may need to look as far back as the beginning of last season in order to understand the cap hit you took when cutting a player.