The safest answer to "is this IW371621 fake?" is to treat any listing without verifiable provenance as suspect until a watchmaker opens the case. The best option for most buyers is a pre-owned genuine IWC Portugieser Chronograph with the full set of box and papers, bought from a dealer who allows an inspection window. That pick rests on four criteria: case and crystal geometry, dial and hand finishing, chronograph movement architecture, and a documented ownership trail. Counterfeiters copy the silhouette well and the small details badly, so the small details are where you spend your attention.
One caution before anything else. Reference numbers in the IW3716 family cover several dial, strap, and bracelet combinations. Confirm the exact configuration of the reference you are looking at through IWC's own reference data before you compare it with anything. A "fake IW371621" verdict is meaningless if the genuine watch was never produced in that combination.
What the Reference Number Tells You
A reference number is a factory order code, not a model name. It defines the case metal, dial variant, and the strap or bracelet fitted at the factory. On the IW3716 series the base watch is the Portugieser Chronograph, a bicompax design where the chronograph registers sit on a clean dial rather than crowding it with extra counters.
That matters for authentication because fakes are usually built from a generic chronograph donor and dressed to look like the reference. The dial layout will be close. The spacing, the printing weight, and the movement underneath will not be.
The Four Checkpoints That Expose Most Fakes
Case and crystal
Look at the lug profile, the polish on the bezel edge, and the curve of the crystal. A genuine Portugieser is finished so that the transition from brushed to polished surfaces is crisp and even on both sides of the case.
- Genuine: consistent brushing direction, sharp lug bevels, crystal sits flush with the bezel line.
- Fake: rounded or wavy lug edges, polish bleeding into brushed areas, crystal sitting proud or unevenly seated.
Dial, hands, and printing
Dial printing is the hardest thing to fake cheaply. Under a loupe, genuine text has clean edges and even stroke weight. Fakes show ink spread, uneven spacing between letters, or a numeral that sits a fraction off its index.
- Genuine: applied indices with sharp facets, hands with a polished bevel and a flat top surface, no dust under the crystal.
- Fake: flat stamped indices, hands that look painted rather than beveled, specks or fibers on the dial.
Chronograph movement and pusher feel
Start and stop the chronograph. A genuine chronograph movement engages with a firm, mechanical snap and the seconds hand starts with no visible jump or hesitation. The reset returns the hand to twelve with a single clean action.
- Genuine: crisp pusher travel, no wobble in the crown, rotor winds with a smooth weighted feel.
- Fake: mushy pushers, a hand that stutters or drifts on reset, a thin-sounding rotor or a quartz tick.
Caseback, engraving, and serials
Engraving on a counterfeit is often laser-etched and shallow, with a font that is slightly too wide. Reference and serial numbers should be readable under magnification, evenly spaced, and consistent with the paperwork. A serial that appears on a stolen-watch registry or that fails a check with an IWC service center is a hard stop.
Paperwork, Price, and Provenance
Documents are easy to print, so treat them as supporting evidence rather than proof. What carries weight is a service history, an original purchase record, and a seller who will let a qualified watchmaker inspect the movement before the sale closes.
- Red flag: a price far below the prevailing pre-owned market for the reference in that condition.
- Red flag: a seller who refuses an inspection, ships from an unrelated country, or pressures a fast decision.
- Red flag: a description that uses the word "replica" or "clone" next to a factory reference number.
Buying a Copy: What You Gain and What You Give Up
Pros
- Lower upfront cost than a genuine or pre-owned original.
- The overall look of the reference is recognizable from across a room.
Cons
- No manufacturer service, no genuine parts, and no warranty coverage.
- Counterfeit watches are subject to seizure at import in the United States under trademark law.
- Resale value is effectively zero, and any watchmaker who opens the case will know.
- Water resistance, accuracy, and finish are unverified, no matter what a listing claims.
For someone who wants the Portugieser look on a budget, the honest route is a pre-owned original in a less popular variant, or a chronograph from an independent brand with real service support. That keeps the money recoverable.
A Ten-Minute Authentication Routine
- Confirm the reference exists in that exact dial and strap combination.
- Inspect the case edges and crystal seating in raking light.
- Loupe the dial printing, indices, and hand bevels.
- Run the chronograph start, stop, and reset cycle three times.
- Compare caseback engraving with the paperwork, then book a movement inspection.
Who Should Buy What
If you are buying to wear and keep, buy a genuine pre-owned watch with records. If you are buying to flip, skip any listing that will not survive an inspection. If you are only chasing the design, a legitimate chronograph from a brand with a service network will serve you better than a counterfeit that cannot be repaired, resold, or legally imported with confidence.