Not all non-reference cards make use of the 8 pin plug. The XFX cards, for example, still follow the reference power delivery design, despite the card having an 8 pin plug. If the VRMs are located between the I/O plate and the GPU die then its reference. If the VRMs are on the other side then it uses the 8 pin plug (Asus, Sapphire, MSI). Check out the Actually Hardcore Overclocking videos on Youtube.