The dB scale is relative to max output. Any -dB level is in relation to max volume and is related to a measure of sound pressure.

Say for example, an absolute volume control was to reach 75dB of sound pressure at about '25' on the 0-100 scale,
and a relative volume control reached 75dB of sound pressure at -25dB, those two points on each control would be equal. Even though the absolute circuit was closer to the lower end of the control's scale, with the relative control closer to the max volume end of it's scale.
This doesn't necessarily mean the absolute volume control has more drive. They are just two different approaches to adjusting that unit's drive.