AA4 in any form are very rare since most were not planned to be produced. Longines also has no actual records of "AA4". They are recorded as 20A. There is no way to count AA4 production numbers from the archives. I believe Patrick Linder was first to publish the AA1-AA4 terminology. We must remember that many different calibers were available after production issues were resolved at the factory for the true keyless 20A.
Also, these AA4 were expensive to produce. Each movement part was hand tuned to fit. These movements were literally hand "finished" meaning the adjustments have to be made to the springs, bridges and plates, not just the jewels, balance, and regulators. AA4 movement parts are not interchangeable. These are non-standard sizes.
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