Visiting GP expert and historian Peter CDE of PuristSPro.com writes:

"GP submitted a total of slightly more than 600 watches to receive the famous Observatory Chronometer award between 1966 and 1967. The "civilian" counterpart, the ChronometerHF model, of course is a certified chronometer itself; just not by the Observatory Neuchatel, but the Bureau Officiels (today known as COSC).
That´s the sensational part in history - GP took serial production pieces made to be worn in daily life on a more random base from ongoing production, instead of submitting especially prepared movements too fragile to be worn and tweaked in performance over years. It´s like winning a Formula-1 race with a serial production car - something which would probably be a similar sensation today." 

A fascinating discussion hosted by GP forum moderator KokChoon Tay!

Source: Horomundi.com