Stateside, yellow lenses were "fog" regardless of fluting.
On the island, FogRangers were clear, heavily and oddly fluted. I am guessing the reason you couldn't get clear FogRangers as factory equipment in the US when they were popular was the clear versus yellow issue.
I know the Jag MK1 and MK2 did not come into US (Canada yes) with FogRangers nor 4-position headlamp switch.
My MK2 came from outside the US late in the game, and it has factory FogRangers and 4-position headlamp switch.
I have used mine in heavy fog.....and many decades of yellow foglamps on my flathead-equipped vehicles, and around here, I would MUCH prefer yellow over clear as far as usability.
Dave