Personally I think they are getting nicked between the factory and the delivery to the customer unless there is a production issue. The ebay merchants are getting them from somewhere or light handed people in dealerships help themselves and are attempting to upgrade their Leons. Just a theory.
VW have two models of the unit, the Discover and the Discovery Pro, they go under different names with Skoda and Seat. It's possible Saggy that you had a fancy one previously with the SSD built in (Plus for the Seat) if not you just cast your eye over and there is a card in SD slot 1 if it's the standard unit. The Seat Navigation Plus looks identical to the standard system except it's got the maps built in on SSD although Seat calls it hard disk it isn't and does more clever stuff faster, and has two free SD slots. You would have been forced to payout another £800 or so in the UK and any financial plans will reflect this.
Easy enough to check you press the navigation button and the map will pop up, no map and your navigation isn't working. What the dealer did with me, which they are probably trained to do when they are sitting in the car before they send you off, is to go through the setup menu of the infotainment screen. Register your phone to the system (bluetooth), USB etc, put your home address in, tune in the radio and setup the time. So if you can't get your home address in, can't see the map when you press navigation, you don't have navigation installed.
Think it was Ruth and one other that were having problems with the installation, that may be when a card had been introduced to the system, pulled out, switched or nicked, then when a new card is put in, it has to be registered correctly by the dealer with their computer plug in tool. They are like viewing cards which are tethered to the box.
The setup wizard is shown below completing A-D below, unless some one has already done this.