Yes and no.
An anthrax weapon, for example, using the Ames strain which was made in Iraq would show little differences from an another weapon using the Ames strain that was manufactured elsewhere.
The same would be true of fissile materials that were purchased from Pakistan or North Korea. The location of manufacture could probably be ascertained but not the country, or group, who had actually put it in a weapon.
I appreciate your premise, yet will decline from agreement. If found where ever, there is always a chain of evidence. May we never find out who is correcto-mundo, by unleased circumstance,for this I pray...