Yes, those are the ones I'm talking about. And the methodology is not the same for every player.
McKelvin is listed as allowing a total of 34 catches for 407 yards. Of those, no more than 13 catches and 133 yards were by his "main coverage assignment." At least 21 catches and 274 yards were by players in his territory other than those listed as his "main coverage assignment."
Antoine Cason is listed as allowing a total of 23 catches for 258 yards. Of those, every catch and every yard was by his "main coverage assignment." In addition, the players listed as his "main coverage assignment" caught at least another 18 passes for 168 yards when Cason wasn't covering them, which tells us that Cason often covered someone other than his "main coverage assignment". So unless Arizona's opponents never even attempted a pass against Cason except when he was covering his "main coverage assignment" each game, there are stats missing from his "metrics."
There are numerous other cornerbacks who also don't have anything listed other than those by their "main coverage assignment" each game -- including Dominique Rodgers-Cromartie, Antoine Cason, Brandon Flowers, Terrell Thomas, Terrence Wheatley and Trae Williams. Is it possible that every one of them spent a good portion of their time covering someone other than their "main" assignment each game but NEVER were thrown at when doing so? That seems unlikely, given than players such as Mike Jenkins, Aqib Talib, Tracy Porter, Charles Godfrey and DeJuan Tribble allowed a significant number of catches -- sometimes even the majority -- when they weren't covering their "main assignment."