When Dr. Crusher orders the computer to monitor Picard's vitals, 1.) She's in a warp bubble-created universe of her own making, where the "rules" were whatever she wanted them to be, even if only subconsciously, 2.) faux-Picard was wearing his combadge anyway and 3.) Picard was the only other "person" on the ship at that point. She could have been effectively ordering the computer to monitor the lifesigns of whomever was wearing Picard's combadge.
In "Bloodlines", there were only a few humans on another otherwise alien-dominated colony, and they still guessed at which human was Jason Vigo.
In "The Game", Wesley was the only person trying to evade the ship's sensors and its crew, making it easy to identify the target as Wes by the process of elimination.