The short answer: a fake IW371759 is either a counterfeit being passed off as a genuine IWC or a replica built to imitate that reference, and the evidence that settles it sits in three places: the caseback engraving, the movement behind that caseback, and the paper trail that ties the watch to a service record. The strongest single route to a decision is a hands-on inspection at an authorized IWC service center, because it is the only route that combines parts-level reference knowledge, movement authentication and a written record you keep. The checkpoints below let you screen a watch yourself before you pay anyone.

Which of the three situations you are in

The search behind this reference usually comes from one of three places, and each one needs a different response.

• Pre-purchase doubt. You found a listing that looks right, but the seller, the photos or the asking price do not.
• Post-purchase doubt. The watch is already on your wrist and something about the finishing, the weight or the chronograph feel is off.
• Replica shopping. You know you are looking at a replica and want to understand which grade you are being quoted and what it will not do.

Decide which one you are in first. Pre-purchase screening costs nothing, post-purchase verification costs money and time, and replica shopping is about setting expectations before you spend.

Checkpoint one: does the reference number check out

IWC reference numbers follow an IW prefix plus a six-digit string, and the digits carry both the model family and the variant. A single wrong digit can describe a watch that was never built, which is why counterfeit listings often garble the number across the title, the description and the warranty card in three different ways.

Pull the exact number from IWC's published catalog or ask an authorized dealer to confirm the case material, dial colour and calibre that belong with it. If the seller cannot match the number to a documented configuration, stop there. No photograph will fix a reference that does not exist.

Checkpoint two: caseback engraving and case numbers

Engraving placement varies with model and production era, so position matters less than quality. Genuine engraving is cut into the metal with crisp edges and consistent depth, and the reference and case numbers stay legible under a loupe. Replicas typically show shallow laser-etched lettering with rounded edges, uneven spacing, or numbers stamped in an order the factory never used.

• Pros: free, needs only a loupe or a phone macro shot, and it catches most low and mid-grade fakes immediately.
• Cons: a high-grade replica can copy engraving well, so a clean caseback proves nothing on its own.
• Use case: run this check on every listing photo before you contact the seller.

Checkpoint three: movement, winding and chronograph feel

Movement numbers, bridge finishing and rotor engraving should match what IWC documents for the reference. Winding a genuine automatic feels damped and even, with no rattle from the rotor when you tilt the case. Cheap replicas give themselves away with a gritty crown, a rotor that spins freely and noisily, or a chronograph that starts with a soft mush instead of a defined click.

Press the pushers in sequence. Start, stop and reset should each feel distinct, and the chronograph seconds hand should snap back to zero without drifting or bouncing. Then watch the minute counter advance at the correct interval rather than jumping ahead of the elapsed time.

• Pros: reveals quartz movements hidden inside automatic-looking cases and exposes cloned movements that no service center will touch.
• Cons: requires hands-on access, so it is useless against a remote listing that only supplies stock images.
• Use case: use it the moment the watch is in your hands, before any money changes hands in person.

Checkpoint four: dial printing and crystal

Look at the printing with magnification. Genuine dial text sits flat, sharp and evenly weighted, and applied indices are polished on their flanks with clean edges. Reproductions tend to show thick or bleeding lettering, indices that sit proud of the dial or catch light unevenly, and subdial rings that are printed rather than recessed.

Anti-reflective coating on a genuine sapphire crystal produces a faint blue or purple tint at an angle, and the dial underneath stays readable from most positions. On replicas, the coating is often absent, uneven, or so heavy that the dial turns milky.

Checkpoint five: case, crown, pushers and clasp

Check the lug bevels, the polish-to-brush transitions and the fit of the end links, which should sit tight with no gaps or rattle. The crown should carry a clean relief logo, thread smoothly and seat flush. On the clasp or buckle, look for consistent engraving depth and a springbar that engages without force. Mismatched finishing and a loose bracelet are two of the most common tells on replica IWC chronographs.

Verification routes compared

If your own checks leave doubt, three routes are available, and they are not equal.

Authorized IWC service center

• Pros: parts-level expertise, movement authentication, an official service record, and a definitive answer on whether the watch is genuine.
• Cons: costs money, takes time, needs an appointment, and a counterfeited watch will normally be refused for service rather than repaired.
• Use case: any purchase where the amount at stake is large, or any post-purchase dispute you may need to document.

Independent watchmaker

• Pros: faster and cheaper, and a good watchmaker can open the case, inspect movement finishing and identify swapped parts on the spot.
• Cons: not every independent knows IWC calibres well, and the opinion carries no official standing.
• Use case: a quick pre-purchase sanity check on a watch you can physically bring in.

Marketplace authentication or escrow

• Pros: convenient for remote deals and useful when you want a third party to hold funds until the watch arrives.
• Cons: photo-based checks cannot verify a movement, and coverage depends on the programme and the category.
• Use case: online listings where you cannot meet the seller and the platform offers the service.

Where fakes of this reference turn up

Expect them in classified ads, social media seller accounts, and marketplaces without an authentication programme. Warning signs repeat: a price well below the market for the reference, a seller who refuses movement photos, stock images instead of dated photos of the actual watch, pressure to pay outside the platform, and a box and papers set that looks newer than the watch. Ask for a photo of the caseback, the movement and the clasp in one continuous shot with today's date written on paper beside it.

If you are knowingly buying a replica

Understand the tiers before you pay. Entry-level replicas often use quartz or unbranded automatic movements with printed subdials and plated cases. Mid-tier replicas copy the exterior more closely but rarely match case finishing or crystal coating. High-grade replicas can look convincing on a wrist and still fall short in movement construction, serviceability and long-term durability, and no IWC service center will repair one. Treat any replica as a costume piece with a finite life, not as an investment, and never accept one sold to you as genuine.

Bottom line

Screen the reference number first, then the engraving, then the movement and chronograph feel. If two of those checks raise questions, walk away or pay for a service center inspection. For a pre-purchase look at a watch in hand, an independent watchmaker is the practical middle option. For anything remote, insist on escrow and fresh dated photos of the caseback and movement before money moves.