Locked Out at T-10
The VTG site is showing interior going for nearly twice it's historical low, but they do not show any balconies available. And that's after the price shot up by over 60% over it's historical low.
So with this cruise as an example, you can see that if you wait too long, you're out of luck.
Some generalizations we might look for in the future would be to watch the room count on the cruise ship site. This isn't an easy task (I had to write a scraper). But one could probably live with just a "feel" for how the room availability was going; certain decks started disappearing from the results, then, in the end, whole chunks of the ship (aft went first, I think). Once there's a noticeable decline, you're probably getting on thin ice. But the VTG site (and probably other resellers), lagged, so the room cruise line room availability can be used as a leading indicator.
The graph shows that trouble starts at 17 days before sailing, when the room count plummeted and there was a price disturbance. Three days later, the cruise ship site quit offering rooms. And 4 days beyond that (at T-10), the reseller quit offering rooms.