^^^^
Judging purely from the filler cap labels it's sounding as if VW have revised the engine to better accommodate 95 RON in later Golfs.
Those with 95 RON labels: What does your GTI Handbook say?
Nothing much really. Says you can use petrol of a higher RON number than is recommended but it makes no improvement on fuel consumption or engine power.
Also encourages the use of fuel containing additives to stop corrosion, keep fuel lines clean etc.
....That's taking a directly opposite stance about RON to earlier cars like mine. Perhaps VW thought that people were too thick to understand the label and think that sales would be effected when they saw 98 RON on the label and thought the car would be more expensive to run.
It surely can't be a generic petrol Golf label because it includes tyre inflation info and surely that's different on the GTI?
Anyway, either V-Power or Tesco 99 is the way to make progress.