Short answer first: the "3399" in those listings is a batch code, not a movement and not anything Audemars Piguet ever stamped on a watch. A fake Royal Oak Perpetual Calendar with that tag is a replica case and dial built around an Asian automatic movement with a calendar module bolted on top. It shows day, date, month, moonphase and a four digit year window. It does not track leap years on its own. Plan on resetting it by hand, and plan on the legal risk that comes with importing counterfeit goods into the US.
Where the 3399 label comes from
Replica factories rotate version numbers the way software companies rotate build numbers. A seller writes 3399 because that is what the batch was called when it left the workshop. It signals a revision: a new dial supplier, a thinner case, sometimes nothing more than a new box. It tells you almost nothing about the movement inside. If a listing leans hard on the number and skips the movement spec, that is your first clue about how the rest of the pitch is going to go.
What the genuine watch actually is
The real thing is the Royal Oak Perpetual Calendar, and the current generation runs Audemars Piguet's caliber 5134, an ultra thin automatic with a perpetual calendar module stacked on the base movement. It knows the length of every month and the leap year cycle, so the date stays correct until 2100 without intervention. Case size sits around 41mm and the whole watch is roughly 9.5mm thick, which is the part replicas struggle with most. The genuine reference trades in the low to mid six figures. Keep that number in your head when someone offers you the same look for a few hundred dollars.
What the replica's calendar really does
This is the part sellers gloss over. A perpetual calendar is one of the hardest complications to build, and the module alone costs more than an entire replica. So the replica world does the sensible thing: it fakes the display, not the mechanism.
- Subdials are usually driven by a modular plate with jumpers and springs. They move and they can be set with pushers, but they do not know February from April.
- The year window is often a disc you advance by hand, or a printed wheel that never changes.
- Moonphase is frequently a 29.5 day disc or, on cheaper builds, a 24 hour disc painted to look like a moon.
- Setting is fiddly. Recessed pushers, soft metal, and a module that does not like being forced. Strip a jumper and the watch becomes a very expensive paperweight.
What to inspect if you are looking at one
Case and bracelet finishing
Run a fingernail along the bevels. Genuine AP brushing and polishing meet at a crisp line with no rounding. On replicas you often see soft edges and polish bleeding into the brushed surface. Tap the bracelet links. A rattle means stamped links, not milled.
Dial and subdial alignment
Look straight down the barrel of each subdial hand. It should point at the same index every time the calendar resets. Off by a hair at 12 o'clock usually means off by a lot at 6.
Movement behavior
Wind it and listen. A healthy automatic is quiet. Grinding, or a rotor that spins like a coin in a dryer, means the module is pressed against the caseback. Check power reserve by leaving it off the wrist overnight.
Water resistance
Assume none. Gaskets are the cheapest part in the build. Do not swim, do not shower, and do not trust a depth rating printed on a caseback.
The legal side, in plain terms
Importing counterfeit goods into the United States is prohibited, and Customs can seize the shipment. That happens at the border, not at your door, which is why sellers push reshipment policies. Trademark owners go after sellers, and occasionally buyers. If you are in the US and weighing this as a purchase, that risk is real and it does not care how good the replica looks on a wrist.
Who this makes sense for
If you want the look of a Royal Oak Perpetual Calendar for a night out and you accept that the calendar is theater, a replica delivers that look. If you want an actual perpetual calendar, this is not one. No version number changes that, and any listing that says otherwise is selling you a story.