Nes 5 screw variant values

Why is there no values for Nes 5 screw variants. Everyone knows the 5 screw variants fetch higher prices than there 3 screw counterparts. Particularly the rares: megaman 1, Mike Tysons punch out, star force, alpha mission, jaws and gotcha. I am a variant collector and have yet to see a variant price guide anywhere and would love to have such a thing for my hobbie