And it is also possible that not even all G-Type stars are appropriate. A Main Sequence star is simply a star whose luminosity is directly related to its temperature. Way Galaxy are Main Sequence stars, and most scientists agree that to be appropriate a star must be a Main Sequence star. Maybe all star types are appropriate. Way Galaxy are singular stars.
Most stars are part of binary or other multiple star systems.
And some scientists believe that multiple star systems are inappropriate for supporting a planetary systems with life. For example, consider the three stars closest to our Sun. And like the Sun, Alpha Centauri is a G-Type star. However, since it is part of a multiple star system it may not be appropriate for supporting a planet with life. Combined together, the three stars are more energetic than just a single G-Type star.