That there where at least plates sensitized up to 1100nm or so is no doubt about.
But about your statement on their practical use in imaging covered objects the way you described.
In previous posts here, the 1000 nm was doubted.
I doubt if I could convince you of viewing a covered object, but there are foil like camoflage blankets that supress the imaging of a hot vehicle (or cannon). You cannot see through this but can see the edges sometimes as they radiate some heat. And, they become quite hot underneath
A plain camoflage blanket would radiate heat. You can see through this latter type of camoflage with IR film. Even so, after the truck or other vehicle left, there would be a hot ground signature that could be used to identify even the vehicle type. This is especially true in many rural areas where you can even track the vehicle to and from several stopping points by the hot spots they leave on the ground.
It is often necessary to cover your stopping points with camoflage after you leave just to cover stop points where you may have created a supply dump.
Basically, all I say can and has been done.