Json provider: parsing inappropriate data

I am processing messages. Each message corresponds to a coordinate, and MOST is in a specific JSON form. The problem is that some naughty messages are in the wrong format (different format where the whole list of coordinates is included in one message).

Ideally I would like to handle both types of messages, but the built-in Parse function for the JsonProvider seems to succeed even when the incoming data is in the wrong format. How can I know ahead of time (before trying to parse) what format my coordinate system is in?

My two data models look something like this:

type ModelA = JsonProvider<"""{      
  "id": "13222",
  "timestamp": 1499329186332.0,
  "latitude": 12.125419,
  "longitude": 15.054884
 }""">

type ModelB = JsonProvider<"""{
    "data": {

        "positions": [
          {      
           "id": "13223",
           "timestamp": 1499329186332.0,
           "latitude": 12.125419,
           "longitude": 15.054884
          },
         {      
           "id": "13223",
           "timestamp": 1499329186332.0,
           "latitude": 12.125419,
           "longitude": 15.054884
         }]
    } 
}""">