Has anything changed with regards to the GTI and WLTP spec when compared to the standard?
Yes, for post WLTP MY19 the normal GTI 230 was dropped, leaving the GTI Performance, which got Rear Camera, Keyless, Lane Assist, Dynamic Light Assist and Traffic Sign Recognition added as standard equipment.
The confusion comes because these options only became standard from mid December build (not registration!) onwards, although VW didn't see fit to tell anybody!). So if it's a MY19 build from Nov to mid Dec then there may be the options missing. My MY19 was a Nov build and arrived at the dealer with the Keyless and Rear View Camera, but it had the other options missing (which form part of a £650 pack). I had that pack cost refunded.