... than L.U.C. 3.96 16/1860, then you may want to ask a Chopard boutique. I did that years ago with a different L.U.C. model and they were able to give me printed data sheets with more detailed information.
... of the data sheets that Chopard sent me several years ago for various gold L.U.C. 1.96 models. You can see the longer reference numbers (e.g., 161860-9009). Note that these data sheets have what I believe is at least one error, "platinum-buckle." ...