See previous response. The aircraft in question were assumed to be crashed and written-off on 9/11 though without physical identification of the aircraft that remains unconfirmed. 9/11 skeptics are not prepared to accept such assumptions here, we are looking for proof as confirmation.
As I have mentioned before, each part of an aircraft has its own unique identification number which can be used to determine the identity of an aircraft. In other words,information that can differentiate a B-757-300 from a B-757-200. Even rivets, wire bundles, cable assemblies, brackets, formers, longerons, stringers, and tubing assemblies have their own unique identification numbers that are pertinent only to B-767-200s and B-757-200 series aircraft.
Each part of an engine can be used to identify the aircraft because it is just a matter of pulling off a part number and then, do a history and accountability check on the engine in question with the airline and engine manufacturer. Let me put it is perspective. You have four vehicles parked in your driveway on January 4, 2013.
1. Red car
2. Green car
3. Blue car
4. Brown car
On January 5, 2013, you have only three vehicles left on the driveway, which are;
1. Red car
2. Brown car
3. Green car
Question is; which car is missing?
It is all very simple and can be applied to aircraft for identification purposes as well. For an example, if you have four B-757s sitting on the tarmac on January 4, 2013, along with their flight history and maintenance records pertinent only to each of the following aircraft identification numbers;
1. B-757-200 #11AA
2. B-757-200, #22BB
3. B-757-200, #33CC
4. B-757-200, #44DD
On January 5, 2013, only the following aircraft are sitting on the tarmac.
Which aircraft is missing? You cannot switch the aircraft because the maintenance records will not match the maintenance evidence on the airframe such as certain repairs that were performed and there will be conflicts with engine records as well.