If you're monitoring an actual system, as opposed to a bunch of simplex or Tier II repeater channels, then the "actual radios" operate the way I described. They don't scan each frequency twice (once for each timeslot), they monitor system frequencies for talkgroup traffic, and if they detect traffic on the talkgroup(s) they're looking for, squelch opens and the traffic is played. The unique identifier for traffic is the talkgroup ID, not the frequency or timeslot.
OTOH, if what you're monitoring is a collection of simplex or Tier II repeater channels, then the talkgroup ID isn't necessarily a reliable way to categorize traffic. You can have the same talkgroup ID reused on multiple frequencies and timeslots, so there's not a lot of value in specifying a talkgroup ID in simplex or Tier II repeater channels.