Short answer

387874 is not a Jaeger-LeCoultre reference number. JLC reference codes start with the letter Q and run to nine characters, for example Q1368420. A six-digit string like 387874 matches the format JLC uses for case serial numbers. It also matches the format used for marketplace listing IDs and auction lot numbers. A watch sold under "Jaeger-LeCoultre 387874" needs two checks. First, work out which of those three things the number is. Second, check the watch.

What 387874 can be

  • Case serial. JLC stamps a serial on the caseback next to the reference. Six digits is a normal length for older pieces.
  • Listing ID. Marketplaces assign internal numbers to listings. Those numbers have no link to the watch.
  • Auction lot. Lot numbers are short and change with each sale.

No public JLC database maps a serial to a model. The manufacture confirms origin through its own archive, and it does this for owners, not for buyers browsing a listing.

How JLC codes work

The reference tells you the model, the case metal, the strap and the dial. Q1368420 is a Master Ultra Thin Moon in steel. Q2548520 is a Reverso Classic. The serial is separate. It identifies one watch. Fakes mix the two. A fake caseback carries a real-looking reference with a serial that repeats across many copies of the same fake.

Numbers on the caseback of a genuine piece are cut into the metal. Numbers on a fake are laser printed, shallow, and lighter than the metal around them.

Movement

Jaeger-LeCoultre makes its own movements at Le Sentier in the Vaud region. Look at the finish.

  • Bridges carry Cotes de Geneve stripes. The stripes are even and parallel.
  • Screws are polished and blued. Slots are clean.
  • Anglage on bridge edges is wide and hand-drawn. Fakes show a narrow machine bevel or none.
  • The rotor is solid gold on most pieces. Steel rotors appear on low-end fakes.
  • Calibre numbers are engraved under the balance or on a bridge. Replicas use a generic automatic movement or a decorated copy.

Open the caseback only if you accept the risk of a scratch. A watchmaker with a JLC parts account reads the movement in minutes.

Dial and hands

  • Printing sits flat and holds a sharp edge. Fakes bleed at the corners of the logo.
  • Applied indexes are polished on all sides. Fakes show a matte flank.
  • Hands are blued steel or polished. A fake seconds hand wobbles.
  • The date window edge is chamfered. Fakes leave it square and rough.
  • Moonphase discs on replicas move at the wrong rate and lose sync in weeks. Genuine gearing runs on the 29.5-day cycle.

Case, crown and crystal

  • Sapphire crystal has no glare ring at the edge. Mineral glass on fakes shows a faint green or grey rim.
  • The crown turns with a light, even detent. Fakes feel gritty.
  • Lug holes and spring bars match the case finish. Fakes leave tool marks.
  • Water resistance is tested at the factory. A fake gasket is unproven.

Reverso checks

Reverso fakes are common. The case flips on two pivots. On a genuine case the flip is smooth and stops with a light click. Fake pivots have play, and the case sits loose in the frame. The back plate on a real Reverso can be engraved, and the engraving is cut, not printed. Case thickness on a fake runs about 1 mm over spec.

Prices

A new Master Ultra Thin Moon in steel runs near $12,000. A Reverso Classic in steel runs near $8,000. Pre-owned pieces trade from $4,000 to $9,000. Any offer under $1,500 for a piece with a claimed in-house movement is not a JLC. Replica prices run $150 to $700.

If you own one

Take the watch to a JLC boutique or an authorized service center. They read the serial, open the case, and confirm the calibre. A service quote is the proof. No photo, no forum post and no listing number gives that answer.

What is unknown

The number 387874 has no published link to a specific watch. Any page that names a model from that number alone is guessing.