One of the frustrations I have had since arriving in country is the lack of K-9 understanding by both military and contractors. It is not anyone’s fault in particular, but it leads to confusion about what the dogs are capable of and what exactly they tell us when they are searching.
Dogs search for odor, not for actual explosives
Dogs are trained to sniff for the odor of explosives. This does not mean that there are actual explosives at the source of the odor. For example, is someone borrowed your car and smoked in it (assuming you had never smoked in it before); the odor of the cigarettes would remain in the car for several days after the car was returned.
You might not be able to tell how much that person smoked in your car or how long before it was returned, just that the car still smells like cigarettes. This is similar to what happens when the dogs “alert” to the odor of explosives. We have no way of knowing (outside of a controlled training scenario) how much explosives were in a vehicle or how long ago they were removed.