Also, unless you can prove that your software is EXACTLY the same after the ground-up rewrite, it will require changes to the voluminous and very detailed train

Also, unless you can prove that your software is EXACTLY the same after the ground-up rewrite, it will require changes to the voluminous and very detailed training materials, necessary to turn a 19 year old with slightly above average AFOQT scores into someone who can fix a complicated airplane on 4 hours sleep a night.