I'm torn on the glasses subject.. On one hand, they've never publicly confirmed that they're hers; of course, I'm sure that is a difficult task to complete without any DNA/fingerprint evidence. We've all agreed they look strikingly similar to the ones she's wearing in the pictures from the beach, but without any DNA or anything I don't think it could be investigated further until they have a solid idea on who they believe is responsible for her disappearance.
& as you mentioned with the purse/cell phone that has yet to be recovered. If whoever dumped the bag, cell phone & sunglasses in that area in the water, there still should have been mud, or a cracked lense.. Something. The photos taken of the glasses after collected by LE make the glasses look practically brand new.. No rust from the mud/water. The phone & bag are obviously long gone, so I would think the sunglasses wouldn't have been found if they were disposed of with the other items. Dawn seems set on the fact those glasses are hers, yet other people say they don't recognize them as Brittanees.
HOWEVER, I'm not sure who else other than teenage girls wear Prada sunglasses!