I've been meaning to publish on this for a while, [...].
To specify that a bit: if you take the base-2 linking scheme construction but only store data in the leaves, you get a more efficient result than any prior published work. That construction is imo what the "optimally efficient accountable time-stamping" should have chosen, but apparently they didn't see it.
That construction is also highly related to a perfect deterministic skip list where the links between layers go into the "wrong" direction compared to a classic skip list: change the links that in the classic construction to always go to the highest possible layer, and you again obtain the base-2 linking scheme with data stored in leaves only.