Didn't mean to suggest that we are suddenly getting 17 segments, rather that those who want to use their god-given 16 now have less flexibility in how to allocate them by continent.

On the grandfather thing, one thing that's not been grandfathered in the past is the right to use an airline (for more than a brief period) after it exits OW. I do expect existing trips will indeed be allowed to add segments as before, but also won't be surprised to find some agents who'll argue the point.