Dear Thomas,
Thank you for your reply.
You say, “When dating a vintage/antique IWC, people tend to be imprecise: Which date is given? Year of production of the movement, year of production of the case, year of sale to a wholesaler, year of sale to a retailer, year of sale to the end customer?”
People do tend to be imprecise. However, the date is clear, and we can and should be more precise.
Making IWC watches began with collecting raw materials and assigning a batch of serial numbers. These dates are recorded in the book about IWC by Tölke and King. Some people take these as showing a movement's production date, but that is wrong. Although the first movements of the batch were finished (final machined, gilded, jewelled, escaped, etc.), soon after the serial numbers were allocated, others were finished later. In the case of a slow-selling calibre, this could be years later. For example, some of the ‘Fishtail’ calibres, 71 Lépine and 72 savonnette, were never finished, and the unfinished materials sold, so the date of their serial number cannot be the date of their production.
Sometime after the serial numbers were allocated, some of the raw materials, usually in sets of 12, were taken from stock and finished into movements. For some customers, such as Stauffer & Co., at this point, the branding required by the customer was applied by stamping before other finishing operations were done. Around the same time, the case would be ordered from the maker. Gold and silver cases were expensive, so IWC did not maintain a stock of cases but ordered them when needed. So, in the absence of other records, a case's production date is a better proxy for the date of making the watch than the movement serial number.
The finished movement was then fitted with a dial and hands, placed in the case, and the stem attached. When the worker finished turning the screw that holds the stem in place and closed the case back, that is when the watch was finished. One might say that this is the date when it was “made”, but semantically, that is awkward. I would say the watch was made during a relatively short period when the raw materials were turned into a finished movement, the dial and hands attached and the assembly placed into a case. After this, the watch would be tested before being dispatched from the factory.
I don't see how the year of sale to a wholesaler (although this would usually be shortly after the watch was finished), year of sale to a retailer, or year of sale to the end customer could be taken as the date of production of a watch.
Watches in hunter cases with lugs soldered on do not make satisfactory wristwatches. The locations of the 12 at the top of the dial, the crown at three and the sub-seconds at 6 o'clock are correct, but the hunter lid defeats the object of a wristwatch, requiring two hands to read the time. This is why wristwatches were made by putting a savonnette movement into a Lépine (open face) case. Rather than try to turn a savonnette case into a wristwatch case by soldering on lugs and removing the lid, IWC (who didn't manufacture cases) would have ordered Lépine cases with lugs attached from the case manufacturers. This could be done in small batches to match the number of sets of raw materials being finished.
You mention an IWC wristwatch dating back to 1899 in the company's museum's stock. Are there any more details of this watch available without visiting the museum? In particular, the details of its manufacture as a wristwatch rather than being later converted from a lady's pocket watch?