Short answer
"3399" is a seller listing code. Audemars Piguet reference numbers for the Royal Oak Perpetual Calendar are five digits in the 25xxx and 26xxx range: 25654, 25820, 26574, 26674. The number 3399 does not fit that format and does not appear in AP catalogs. The same watch shows up under other numbers on other sites. Ask the seller for the reference stamped on the caseback and expect no answer.
What the real watch does
The Royal Oak Perpetual Calendar 26574 measures 41mm across and 9.5mm thick. It runs calibre 5134, a 374-part automatic with 38 jewels and a 40-hour power reserve. The calendar tracks day, date, month, week number, moon phase, and leap year. It corrects for 28, 29, 30, and 31 day months and does not need a manual reset until 2100.
What replicas do
- Movement: Miyota 9015, Seagull ST19, or a decorated Asian automatic with a cosmetic calendar plate. No leap-year wheel.
- Subdials: month and leap-year discs sit on the dial as printed graphics or move only when the owner turns the crown.
- Date change: most skip the February correction. The date reads 31 on a 30-day month until set by hand.
- Thickness: 11mm to 13mm against 9.5mm on the genuine watch.
- Moon phase: one printed disc on a 24-hour gear, not a 29.5-day train.
- Finishes: bracelet brushing, bevels, and the tapisserie squares are the first tells. Squares on replicas sit shallow and uneven at the edges.
Checks before paying
- Ask which movement. A "Swiss ETA" claim on a perpetual calendar listing does not hold up, because ETA builds no such calendar module.
- Request a video of the date passing midnight on the 28th. A working perpetual calendar advances on its own.
- Request thickness photos with calipers on the case flanks.
- Ask how the leap-year subdial moves. If the seller says it moves with the crown, the mechanism is decoration.
- Ask case metal. Gold-plated replicas use brass or tungsten, and a 41mm gold case weighs more or less than the originals depending on which.
Price bands
Listings tagged 3399 run about $180 to $900 based on movement and plating. Below $150 the watch holds a quartz module or a basic automatic with printed subdials. Above $900 the markup covers packaging and photos, not parts.
US customs and law
Counterfeit watches are subject to seizure under 19 U.S.C. § 1526. CBP publishes seizure totals each year. Trafficking in counterfeit goods is a criminal offense under 18 U.S.C. § 2320. Buyers seldom face charges. Sellers and importers do.