TV175 top end speed

I’m puzzled, doesn’t take much but? “Google” says the series 2 175 has a top end speed of 64mph whereas series 3 175’s only 60mph.
I’ve just returned to scootering and re-learning. I always thought that the series 3 was an upgrade on 2 so how can this be. I’ve researched on various websites but information seems to vary. Any pointers from the professionals out there will be useful.
Thanks
I’ve just returned to scootering and re-learning. I always thought that the series 3 was an upgrade on 2 so how can this be. I’ve researched on various websites but information seems to vary. Any pointers from the professionals out there will be useful.
Thanks