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Actually, it's a rather interesting story. The original factory was called KW, or Kuvarsit Watch. Then around two years ago, the factory changed its name to V6F as it wanted to establish its separate identity. Then late 2016, early 2017, V6F decided to separate its operations into two sub factories, VSF and XF. VSF was supposed to be used for Panerai, XF for other brands (although this does not seem to be adhered to as XF has released PAMs as well).
Back OT, the PAM213 Rattrapante is one of those grails because of the working functions and the rather extremely limited release, like dadog13 said only 80 were made (movement was expensive and it had a low yield, resulting to low margins even with the high $600 selling price prompting the factory to stop production) and even less were sold to forum members.