To be clear, there's no recall for any of these automakers, yet. The government is simply asking for a full list of vehicles that each of them have with Takata-supplied inflators containing ammonium nitrate propellant. The agency is concerned this substance could play a roll in the ruptures. "NHTSA is considering not only whether to issue an administrative order that would coordinate the remedy programs associated with the current Takata recalls, but also whether such an order should include expansion of the current recalls," the letters say. All seven can be viewed, here.
From a report supplied by Takata, the government already knows that the company supplied 887,055 inflators with ammonium-nitrate propellant to VW and 184,926 of them to Tesla. In an incident during the summer, a side airbag allegedly burst in a 2015 VW Tiguan.
In early September, NHTSA put out a revised report that there were 23.4 million inflators to be replaced in 19.2 million vehicles in the US. An earlier accounting from the agency had about 34 million of the parts in 30 million cars. High humidity is still believed to be among the biggest risk factors for the ruptures. Although, if ammonium nitrate also gets the blame, some already recalled models might need to be repaired again.