The short answer

A fake IW371775 is a counterfeit sold under a real IWC reference number. The IW3717 block belongs to IWC's Pilot's Chronograph Automatic family: a 42 mm steel chrono with two subdials, day and date at 3 o'clock, and a soft-iron inner cage around the movement. If you already have a watch with that number engraved on the back, the number itself proves nothing. Fakers engrave whatever moves product. Real authentication comes down to the movement, the dial printing, the case finishing, and the paper trail.

What the number actually refers to

IWC builds reference numbers as IW plus six digits. The first digits narrow the family, and the final digits encode the dial, case metal, and strap combination. IW3717 is the Pilot's Chronograph Automatic line that ran through the 2000s and 2010s, the 42 mm one with day and date at 3 and the classic flieger dial. Because the last digits change with every dial variant, two honest IW3717-prefixed watches can look completely different. That is also why a faker can print almost any number in that block and find a buyer.

If the exact reference you are offered does not appear in IWC's own listing for the model, that is your first red flag. IWC publishes case size, calibre, and materials for its references, and a service center or authorized dealer can tell you whether a specific case number was ever produced.

Where counterfeits fall apart

The movement is the hardest part to copy at a low price. Genuine 3717 examples run the IWC calibre 79320, a heavily modified Valjoux 7750 with day and date, 28,800 vibrations per hour, and roughly 44 hours of reserve. A counterfeit might use an unbranded 7750 clone, a cheaper chronograph module, or quartz. That difference shows up on the wrist, not just under a loupe. Push the chrono buttons. A real 7750-based watch has a firm mechanical snap and a reset that slams home. Quartz fakes tick the small seconds once per second, while a mechanical movement sweeps.

Dial details matter more than most buyers expect. On the genuine watch the IWC wordmark is applied, sitting above the dial surface with a clean shadow line. Fakes print it flat. The date and day fonts are crisp and correctly sized. The minute track is even. Indexes line up with the subdials and the center of the hands. On a fake you can usually find one element sitting half a millimeter off, and once you see it you cannot unsee it.

Checks that settle it fast

  • Case number behavior. IWC engraves a reference and a case number on the back. Fakers often reuse one case number across a whole run, so if two listings show identical case numbers, both are counterfeit.
  • Weight and feel. A real steel case has heft and a cold first touch. Plated alloy feels light and warms up fast. Rough test, not proof, but it filters out the cheapest junk.
  • Subdial function. Confirm the 12 o'clock subdial counts chronograph minutes and the 6 o'clock subdial runs the seconds. Fakes sometimes wire both to the chrono or leave the seconds dead.
  • Crown and pushers. Screw-down crown with clean threads, pushers that return without wobble. Mushy pushers mean a cheap movement or a worn case tube.
  • Crystal. Genuine examples use sapphire with anti-reflective coating on both sides, which is why the dial nearly disappears at some angles. Mineral-glass fakes reflect noticeably more.

Paperwork and history

Boxes, booklets, and warranty cards get faked too, and usually worse than the watch does. A genuine card from an authorized dealer carries a stamped date and a case number matching the watch. Blank cards, mismatched numbers, or a seller-issued certificate of authenticity are meaningless. IWC service records are the strongest proof, since a watch that has been through the manufacturer or a reputable watchmaker leaves a trail.

Price tells you a lot

A used Pilot's Chronograph in the 3717 family trades in the low four figures depending on condition and completeness. An offer at a few hundred dollars is a counterfeit, a stolen watch, or a scam. There is no honest version of that deal.

US legal reality

Counterfeit watches are illegal to import into the United States. Customs and Border Protection seizes them at ports and mail facilities, and the buyer eats the loss. Selling counterfeits is trademark counterfeiting under federal law, with civil damages and criminal exposure attached. Buying a fake is not a victimless shortcut. It is a seized package waiting to happen.

Bottom line

If you want a real IW371775, buy from a dealer or a private seller who will let a watchmaker open the caseback, and verify the case number with IWC before money changes hands. If the seller refuses any of that, you already have your answer.