I had a perfectly good dash, changed it for a nismo lcd and ej1 ecu, once i put the new dash and ej1 in for some reason both the dash and my avcr starting reading half the speed i was doing, the wiring for the ej1 was taken off the loom just before ecu, so was the avcr, the normal speedo in the dash was taken from the factory loom.
The main concern was the avcr, it worked perfectly before and now was reading the same as the dash, when i put the ej1 in i had the jumpers wrong, thought i may have fried the speedo sensor so i got a new sensor, didnt make a difference, in the end the ej1 some how f**ked up the readings from the afm, $1000 later finally found that the ej1 was making the car run like shit and changed back to the normal dash, once i did the speedo and avcr were reading normal again.
My conclusion is that the speedo reading goes through the dash to the ecu, if there was one sensor for the dash and another for the ecu then the only thing that would have read wrong is the guage in the dash not the ej1 display in the dash, i also highly doubt they would bother using two types or speed sensors, if they did have speed sensors on the wheels and the gearbox then the 33 would also have traction control, maybe the 34 has both but i dont think the 33 does.