There is actually no need in asking anyone. There are required inspections and replacements of parts on each plane at regular intervals. Take the flight timetables, list the planes, calculate a total number of work hours, and you get the number of spare parts required after a given number of days or months. If a grounded plane is the only source of some critical complex part, and you are confident enough there was no smuggling across the border (because you own/control the supply chains), you can guess that it was used that way.