Short answer

A fake Jaeger-LeCoultre 1398420 fails three checks: caseback engraving depth, movement finishing, and the pairing of the serial number with the reference number. Genuine JLC watches run an in-house calibre with hand finishing. Counterfeits use a decorated ETA or Seagull base, or a quartz module hidden behind a solid caseback.

What reference 1398420 is

Jaeger-LeCoultre reference numbers in the 139.84.20 group belong to the Master series. The brand catalog is the only source for the model name, case diameter, and calibre number. Confirm those three data points before you compare a watch to this reference. We could not verify one single model name for 1398420 from public sources, so treat any seller who names it without a catalog match as a risk.

Price bands help. Stainless steel Master models list between about $8,000 and $12,000 new. Used examples trade between $5,000 and $9,000. Counterfeits sell for $150 to $700. A working watch at $900 is not a bargain.

Caseback and engraving

  • Genuine lettering has sharp inner walls and even depth. Run a fingernail across it and you feel a cut edge.
  • Fakes show laser etching that looks flat, or acid etching with soft, rounded edges.
  • Caseback screws on genuine pieces are slotted flat heads with polished tops.
  • The serial number sits near the reference number. Both are unique. A repeated serial across two listings means one is false.

Movement

  • Master series watches use in-house calibres from the 899, 925, 938, or 939 families.
  • Genuine rotors carry Cotes de Geneve stripes, an engraved JLC logo, and often 22k gold mass.
  • Fakes use rhodium-plated brass with stamped stripes and wrong letter spacing in the logo.
  • Check beat rate. Genuine calibres run at 28,800 vph (4 Hz). A phone timegrapher app counts this in one minute.
  • Jewel count on the bridge must match the calibre the seller claims.

Dial and hands

  • Applied indices on genuine dials sit in drilled holes. Glue blobs around the base mean a fake.
  • Dial print is thin and flat. Thick ink and halos around letters mean a fake.
  • Date numerals follow a JLC typeface. Generic ETA date wheels show a different shape.
  • A moonphase disc shows a shaded moon with craters on genuine watches. A flat yellow circle means a fake.

Papers and box

Master Control models ship with a 1000 Hours Control certificate. The warranty card serial must match the caseback serial. Booklets are printed on heavy stock with sharp type. A box alone proves nothing, since boxes are sold on their own.

Five minute check

  1. Photograph the caseback at an angle with side light. Compare engraving depth.
  2. Ask for a movement photo with the caseback off. Refuse to buy without it.
  3. Match the caseback serial to the paperwork.
  4. Search the reference on the brand site and compare specs.
  5. Pay a watchmaker $30 to $60 to open the case.

Counterfeit and replica are different words

A replica is sold as a replica. A counterfeit is sold as a genuine watch with false papers. Only the second one is fraud. Sellers who use the word genuine while shipping a replica are the problem, not the watch itself.