Short answer
A. Lange & Söhne does not list a Lange 1 reference numbered 1920. Lange 1 references run in the 101.xxx and 191.xxx ranges. A listing that reads "Lange 1 1920 platinum" is using a seller code, an auction lot number, or an invented number. The watch behind that label is a replica.
What the replica is
Platinum Lange 1 replicas come from Chinese workshops. The case is 316L stainless steel in most samples, plated to look bright. Some sellers use a tungsten alloy to add mass. Platinum has a density near 21.45 g/cm3. Steel sits near 7.9 g/cm3. A steel case of the same volume weighs about one third of a platinum case.
What the genuine watch does
The Lange 1 launched in 1994. The dial is off-center. Time sits at the left. The outsize date sits at the top right. A power reserve scale sits at the bottom right. The date uses two separate discs. The movement is hand-wound. The current calibre runs 72 hours on a full wind. The case measures 38.5 mm across.
Where replicas fail
- Date: one disc with printed numerals, not two discs with a cross mechanism.
- Movement: plated brass plates with laser etching. No Glashütte ribbing cut by hand. No engraved balance cock.
- Weight: a steel case in platinum finish carries far less mass than platinum 950.
- Dial: thicker print lines and uneven spacing on the power reserve scale.
- Caseback: shallow engravings, and a 950 stamp on steel.
Inspection checklist
- Ask for the head weight in grams.
- Ask for a macro photo of the date window during the change.
- Ask for a photo of the balance cock and its engraving.
- Check the reference number against the Lange catalog.
- Check for a Pt950 stamp and the metal color of the caseback.
Price
Replica Lange 1 listings sit between about $300 and $900. The spread tracks the movement and the metal claims, not the fit of the copy. No factory reproduces the L121.1 calibre. A used platinum Lange 1 sells in the tens of thousands of dollars. Auction results move with the market.
Bottom line
1920 is not a Lange reference. Treat any listing with that number as an unverified claim. Judge the watch on the movement, the date mechanism, and the case metal.