"Throttle position" and "pedal position" are different things. On some cars, there is no direct coupling between the two: the pedal simply controls a potentiometer and the throttle is controlled by the ECU.
A single throttle plate can have up to three throttle position sensors (A, B, and C).
"Absolute throttle position" means the TP is reported as "seen" by the ECU. On most cars, the lower value will be above 0%, and upper value will be below 100%.
"Relative throttle position" means the "learned" TP position. The ECU calculates the voltage offset for the closed-throttle position, and uses it as the 0%. If the offset voltage is higher than 0V, then you never get to 100% even for WOT.
Clear as mud?