i had a standard chrono-matic from 69 until a few years ago and had never
seen one like yours, but only last night saw another one on the bay.
the story behind all the NOS ones popping up is that when Breitling were
changing hands one of the staff or management effectively took most of the old
stock and put them in safety deposit. they came out a few years ago to much
acclaim. they all needed servicing of course after 20+ years in a bank. i should
have bought one then but i had a chrono-matic, cosmonaute and spatiographe at
the time and didnt want anymore.
it would be great to find out that there were only 20 made, but as you say,
no real proof.
as for NOS condition, just get it on the wrist and wear it. watches get
scratched and it adds character.
best
Graham