In Mk1 -- and think Mk2 also , they had two diffy calibrated speedo heads.
On the face above or below the needle there is a number like 1340 or 1540 ,,, - i'm shooting this from memory. But that number is the calibration.
Thats how 2 cars with different ratio trannys can use the same color gear.
They would have 2 diffy speedo calibration numbers on their dials.
Between the different speedo gears - and the different gauge calibrations - it gave them a lot more flexibility/adjustability in production with fewer parts.