Short answer

IW93870 is not a reference number IWC uses. Current IWC references read IW plus six digits, like IW328901 or IW371617, and older models follow a shorter, caliber-based pattern. When a listing shows IW93870, you are looking at a replica, or at a seller who copied a number from another fake listing and never checked it against the brand. The useful question is not what IW93870 is. It is how to tell whether the watch in front of you is real.

What gives a counterfeit away

Fakes fail on the same handful of details, and they fail in person more than in photos. Ask for sharp, straight-on shots on a plain background, then compare them side by side with the same model on IWC's own site.

• Dial printing. Genuine text sits crisp and level, with even spacing between letters. On copies the font drifts, the markers sit a hair off center, and the date window edges look rough under a loupe.
• Case finishing. IWC brushes and polishes in defined zones with a clean line between them. Replicas blur that line, or polish the whole case and call it a day.
• The crown and pushers. Threads should feel smooth, not gritty, and the crown should seat flush against the case.
• Caseback engraving. Reference numbers, case numbers, and movement numbers should be cut into the metal, not printed on it, and they should all agree with the paperwork.
• Weight and sound. A real IWC has heft. A cheap automatic rotor spins with a loud, tinny whir that you can hear across a quiet room.

Reference numbers are easy to fake, records are not

Anyone can stamp six digits on a caseback. What a counterfeiter cannot produce is a matching record. Look up the reference on IWC's site or ask an authorized dealer to run the case number. If the model, the dial color, and the movement listed in the archive do not match the watch in your hand, stop there. Sellers who dodge a caseback photo, or who send one that is soft, angled, or cropped, are telling you something.

Do the price math first

A stainless IWC with an in-house movement does not sell new for a few hundred dollars, and it does not sell used for that either. Deep discounts on current models are the oldest signal there is. So is a box and papers set that looks laser printed, with a warranty card that has no dealer stamp and no purchase date.

If you already bought one

Move fast. Counterfeit watches can be seized by U.S. Customs and Border Protection on import, and marketplaces and card networks have their own rules about counterfeit goods. Open a dispute while the listing page is still live, screenshot the description and every message, and photograph the watch from all sides before you send anything back. Keep the return tracking number.

Bottom line

A number that does not exist in the brand's catalog is the first clue, not the last. Judge the watch on its finishing, its records, and its price. If two of those three look wrong, walk away.