Are all the purple sapphires in this collection star sapphires?

No. Some stones in this collection show six-ray asterism and some do not. Each product page states what its own GIA report records, including the cutting style.

What does a GIA report confirm on a purple sapphire?

A GIA report states the species and variety, the weight, measurements, shape, colour and cutting style as findings, and records any heating under Additional Results. Where it gives a geographic origin, GIA prints that this is an expert opinion.