Short answer

A fake IW329151 fails three checks: the reference number, the caseback, and the movement. Start with the reference number. IWC reference numbers use the format IW plus six digits. Open IWC's own catalog and search IW329151. If IWC does not list the reference, the watch is not an IWC. No box, card, or photo changes that result.

Why the reference number comes first

Replica sellers put real reference numbers on cases bought from a third party. A 3291 case can hold a dial from a different model. Four items have to match the same reference: case diameter, dial layout, movement caliber, and strap or bracelet type. A mismatch on one item is enough to stop.

Caseback and engraving

  • Reference and serial numbers are engraved, not printed. Stamped numbers show a soft edge under a 10x loupe.
  • Both numbers use the same font on an authentic case. Fakes mix fonts.
  • Engraving depth is even. Laser etching looks pale and shallow.

Movement

IWC movements carry a signed rotor and decorated bridges. Fakes use stock movements with a printed plate over the top. Put the watch on a timegrapher. Stock movements in replica cases run at 21,600 vph. IWC calibers in this range run at 28,800 vph. Ask for a clear photo of the movement before payment.

Papers and warranty

An authentic IWC ships with a warranty card that shows the same serial as the case. The card carries a date and an authorized dealer stamp. IWC runs warranty registration through My IWC. Registration extends coverage from 2 years to 8 years. A seller who cannot register the watch raises a question.

Parts that copies get wrong

  • Crown threads. A real crown shows resistance at the last half turn.
  • Lume. Applied markers sit level with the dial face. Copies sit high.
  • End links. Gaps of 0.2 mm show on authentic parts.

What photos cannot prove

Photos do not show weight, crown threads, or movement finish. Measure the case diameter with calipers. A 42 mm case measures 42.0 mm, not 41.4 mm. Weigh the case head with no strap and compare the number against an authentic example of the same reference.