This diagram of the Lincoln second floor appears in Seale’s two-volume WH book. It shows the old west stair as a dual initial rise and a central rise to the second floor. But we know from photographs of the grand stair that by the 1890s it was a single initial rise at the right, a left turn, then a single rise to the second floor.
However, I don’t recall ever reading about that stair being renovated from dual to single. The question is, are we sure the dual rise stair was ever built? And when was it renovated to the single stair we see in the photos?