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You are confusing the coefficient of drag (Cd), which is what the graph is of, and BC
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Nothing matches the test projectile except the test projectile.
Variation shows up even with simple size scaling of the test projectile.
The use of all the differnt test projectiles has been to try and find a better curve with less variation with other shapes.
* G1 or Ingalls (by far the most popular)
* G2 (Aberdeen J projectile)
* G5 (short 7.5° boat-tail, 6.19 calibers long tangent ogive)
* G6 (flatbase, 6 calibers long secant ogive)
* G7 (long 7.5° boat-tail, 10 calibers tangent ogive, preferred by some manufacturers for very-low-drag bullets[10])
* G8 (flatbase, 10 calibers long secant ogive)
* GL (blunt lead nose)
And even more, but that is the quick to find wiki list.
It is an absolute bear to even model the test projectile (with lots of data to compare the model) with six and seven degree of freedom aeroballistic software.
You can tweak the model to match one projectile, but it no longer matches the others adequately.