D' connects the long staircase near B16 with the staircase from A4, and the open area off of B9. E is reached by a secret door in the trunk of the Tree in D3. Had intended to expand these levels as play on level B progressed. However the TPK on level A, followed by a lifetime ban on this dungeon from She-who-must-be-obeyed, rendered that effort moot.
P.S. for an interesting corollary of the problems this dungeon encountered read this review of Death Frost Doom .
Unfortunately, sometimes even the best sounding dungeons on paper do not click with the players in the field. This dungeon did teach me a lot about player-DM interaction. Most of my modern dungeons are a lot less scripted and adapted on-the-fly to suit the players motivations. Good for playing, bad for producing a module for publication and universal appeal.