Does "perfect alignment of cart" eliminate 100% ?

Dgad, that is an excellent point. Speed stability can also be the last piece to eliminating sibilance.

I did notice that playing with the alignment did help reduce the IGD but its not 100percent eliminated.
Does incorrect anti-skate setting also causes IGD ?

Some arms are more affected than others, yes. Mistracking in the inner grooves might also be caused by the mechanical resonance of the arm/cartridge being slightly too high.

Electrical loading of the cartridge can help too.

Some preamps will exhibit a distortion that sounds a lot like mistracking. This seems to show up in less expensive solid state units that use excessive feedback.

An interesting passage from Keith Howard's "Arc Angles" article in the March "Stereophile:"

"In fact there is another vital parameter, namely linear groove speed (that is, the speed at which the groove passes the stylus), which varies by a factor of about 2.5 from the outermost to innermost modulated groove radius of an LP. LTED (lateral tracking-angle distortion), it turns out, is inversely proportional to linear groove speed, and so the same LTE at the innermost modulated groove radius of an LP will result in about 2.5x higher distortion than the same angular error at the outermost modulated groove radius."

Does this mean that those who have zero inner-groove distortion also have less-than-zero distortion at the outer grooves?

-Bob

It's called "un-distortion", a world where everything becomes crystal clear and transparent. They use it at airports.