Even at its best, Date Your IWC can only offer you tentative results.
If you need a truly reliable dating of your IWC timekeeper, there's no other way than to order an archive extract from IWC.
The site openly states they've matched more than 100,000 happy couples and that they assist their clients with legal and visa support, if necessary.
However, you'll notice very quickly most of the members are female and Phillipino.
The availability of sources dictates that the application works best with vintage watches produced prior to 1975.