And we shouldn't ignore simple fact of evolution both in material and use/placement. If something works use it. If something doesn't work (or doesn't work anymore) change it or stop using it.

I see tendency to draw conclusion: "IED are getting more sophisticated therefore they are receiving foreign help. IED are getting more effective therefore they are receiving foreign instructors." But it could be simple evolution. Wire detonated bombs are easy to spot so they change to command-detonated. Certain frequencies are getting jammed so they change it or use different source of command signal. Armored vehicles are hard to destroy so use more explosive. etc

It's not only the US that learns.