Vital point method with one point eyes

Reference diagram  

This position is taken from Gokyo Shumyo, Section 1, Problem 25. White to live. Let's try to make a one-point eye with as few moves as possible.

Diagram 1  

Adding two stones.

Diagram 2  

Adding two stones.

Diagram 3  

Adding three stones.

Diagram 4  

Adding three stones.

Reference diagram  

Looking back at the reference diagram, points a and b occur in three of the four diagrams. Both are vital points, but a is more valuable than b, because a occurs in both diagrams with two stones. This reasoning can easily be quantified.

Conclusion: a is the vital point.

Dieter Verhofstadt

Reference diagram again  

Is it a correct reasoning that the vital point can be seen as the connection between shared liberties of different groups (marked by )?