Basically what happened with these buoys is they melted out in September and then the pack consolidated and froze them back in a few weeks later. However the ice never achieved any free-board...
How can you tell freeboard from IMB data - it doesn't show sea level. The initial zero point is the top surface of the ice as and when the buoy was placed. At that point, the water levelwould have been at around -20cm, since 20cm freeboard is what you'd expect for a floe that's 1.7 metres thick.
As the ice thickened from below, note that the buoy remained frozen in place, so the zero point (ice surface) doesn't change even as the floe thickens and rides higher in the water. Conversely, when top melt starts, the ice surface goes down relative to the buoy, reaching about -25cm in early August. This doesn't mean the floe was underwater at that point - as the surface layers melt away, the remainder of the floe will inevitably have risen in the water by simply physics.
When the buoy melted free in September it will have bobbed freely in the hole (giving unstable readings) until it re-froze. After re-freeze, the new zero is at an arbitrary point depending on how the buoy happens to have ended up relative to the ice surface. Once it freezes in place, that resets a new zero level at the (new) ice surface, which then remains fixed even as snow accumulates above.
Crucially, you have no data as to the water level, and thus cannot tell what the freeboard is, whether the floe is submerged, or any such conjecture.
Edit: Also, why are you blithering about data "censorship" from the two other buoys? They were placed in September, but so far there's been no output from them (except maybe GPS? There's a supposedly "current" position from early December...). Possibly they were dead on arrival and they're just not giving data. Maybe they weren't designed to generate data during the winter, but they're conserving battery power so as to give accurate data once they start receiving sunlight in the spring. We just don't know, and leaping to accusations of censorship is plain ridiculous.