Then maybe instead of using a texture for the transparency they changed the transparency within the shader itself and just changed the alpha values there.
When importing the plane to blender the alpha value is 0.01 in Blender, unfortunantely I cant see what textures are attached in Blender. But I think they just drive the glass transparency with the A value.
So its not just the scratches you try to remove , but also the reflections?
Just checked the DA62 sample plane from the SDK also doesnt use any texture for the windshield.