The short answer
Jaeger-LeCoultre does not list 1398420 as a reference number. It looks like a serial number, the kind stamped on the caseback or movement of a vintage piece. That matters, because a serial number is not a model name and it does not prove a watch is real. Counterfeiters stamp serials too, and they often pick numbers that look right for the era they are faking.
So the honest answer to "is 1398420 fake?" is that nobody can tell from the digits alone. You have to look at the watch.
Reference vs serial: the difference
JLC uses two identifiers. The reference, sometimes called the case number, describes the model. On modern watches it looks like Q2548520 or Q3858522. On older pieces it is a group of digits separated by dots, such as 270.8.62. The serial is the individual number of that specific watch, and on vintage JLC it is usually six or seven digits, stamped inside the caseback and repeated on the movement.
1398420 fits that serial pattern. If a listing calls it a reference, the seller either does not know the brand or is hoping you do not.
Why a serial alone proves nothing
- JLC does not run a public serial lookup. There is no website where you type a number and get a model.
- Serials get reused by fakers, and a swapped caseback can carry a real number on a fake watch.
- Vintage paperwork is easy to fake, so a card that matches the number is weak evidence.
What I look at instead
- Dial printing. JLC fonts are thin and even. Copies show thick, uneven letters, a fat "Jaeger" or a crooked "LeCoultre" under the twelve.
- Proportions. Look at lug shape, bezel width and crown size. A Reverso that looks chunky, or a Master Control that looks thin at the lugs, is a warning.
- Hands and markers. Blued steel should be deep blue, not painted. Applied markers should sit flat and line up with the printed track.
- Caseback engraving. Real engraving is crisp and shallow, done with a die or laser. Fakes often look etched, grainy or too deep.
- Crystal and date. A cyclops that magnifies unevenly, or a date that sits off center, is common on copies.
Movement tells
This is where most fakes fall apart, and where photos usually stop. JLC makes its own movements, so an authentic watch should not contain an ETA, Sellita, Miyota or Seagull base. Fakers decorate those movements with JLC-style rotor engravings, blued screws and Cotes de Geneve stripes. The stripes are usually too wide, the screws are painted rather than heat blued, and the engraving is shallow. Ask for a clear photo of the balance, the jewels and the rotor edge. If the seller refuses, treat the watch as fake.
On a Reverso, remember the movement sits in a flipping cradle. That mechanism is hard to copy well. Check that the case flips smoothly and sits flat when closed.
Getting a real answer
- Ask the seller for the full reference, the serial, and photos of both case sides plus the movement.
- Compare the reference against JLC catalog pages for that model line.
- Take the watch to a JLC boutique or an authorized service center. They can confirm the movement and, for older pieces, request archive information.
- Pay for an independent watchmaker's inspection before money changes hands. It costs far less than a bad purchase.
Before you buy
Price is the loudest signal. A steel JLC at 20 percent of market value is not a bargain, it is a warning. So is a seller who only meets in parking lots, has no history, or pushes you to decide fast. Buy from a source with a written return policy and a written authenticity guarantee. If the watch is vintage, ask what was serviced and who did the work. A real JLC with service records holds value. A copy holds nothing.
Treat 1398420 as a starting point for questions, not an answer. The number can be real and the watch can still be fake.