ok , lets try to interject a bit of logic here ,
IF and thats BIG if , they were going to " switch the planes " and kep it flying - isnt a change in serial number and registration certification
the FIRST thing you would think off
admittedly there is no precedent i can think off gor such " plane ringing " - but it is distressingly prevalant in shipping circles
and as for cars and commercial vehiles - heck " car ringing " is the number one industry in some towns

.... like liverpool ;;; cough ;;;
and EVERYTIME - the first thing they do is change the number plates , VIN plate and give it a respray
why would anny attempt to ring a plane be an different ????
as has been noted - planes lost in mundane crashes pree 9/11 stayed " on the book " for years after .
so why do you expect the 9/11 planes to have been treated differentlt ???
the most innocent explaination for this policy that springs to my mind is - is it a tax scam ?? or accounting trick - to keep a lost plae listed as an
asset ?? for as long as possinle ?
any one with accounting experience confirm or deny this ?