Short answer
IW371478 belongs to the IWC Portugieser Chronograph family on the 3714 platform. That platform runs a 40.9 mm case, a 12.3 mm case height, and a 20 mm lug width. The movement is IWC calibre 79350, a rebuilt Valjoux 7750 with a 44-hour power reserve. Subdials sit at 12 and 6 o'clock. Water resistance is 3 bar. Steel examples sell pre-owned at $5,000 to $8,000 USD. Copies sell at $200 to $600.
The reference number is the first test. IWC lists the references it produced. If the number in a listing does not match the case metal, dial color, and movement shown in the photos, the listing is wrong. No other check matters until that one passes.
Caseback and reference number
Ask for a straight-on photo of the caseback with the light behind the camera. Genuine engraving on this family is deep, even, and sharp at the edges. Copy engraving is shallow and reflects light in flat patches. The serial sits on one line. A mismatch between the caseback number and the number on the paperwork is a fail.
Movement
Genuine calibre 79350 shows Geneva stripes, blued screws, and a signed rotor. Asian 7750 copies use printed text in place of engraving and a rotor with a dull finish. One caution: the 7750 base has a wobbling rotor in both real and fake watches, so rotor wobble tells you nothing. Look at finish and markings, not sound.
Dial, hands, and case
Check the applied indices for level seating and polished edges. Check the IWC and Schaffhausen print at 3x magnification. Copy print has soft edges. The date window should be clean cut with a block date font. The crown should carry the IWC mark and screw down without grit. Case bevels on a genuine 3714 are polished and the lines run straight.
Price and seller behavior
Steel IW3714 watches trade at $5,000 to $8,000 pre-owned. Gold cases run above $12,000. Anything under $2,000 is a copy, a franken, or a stolen watch. Wire transfer only, no returns, no escrow, and a rushed deadline are signals on their own.
Papers, box, and service records
IWC ships this reference with a numbered warranty card, a booklet, and a leather inner box. Ask for the original invoice and any service invoice. An IWC service invoice lists the reference and the serial. Call an IWC service center with the serial and ask them to confirm the record.
If you already bought one
Get a written opinion from an IWC service center or an independent watchmaker. That costs $75 to $200. Counterfeit watches cannot be imported into the United States and cannot be sold there. Ownership alone is not the offense. Import and sale are.