Very enjoyable in the end, though one or two ambiguous surplus letters held me up for a while. Can become a bit like the Only Connect missing vowels round (eg 54A, with a different abbreviation I had E as the extra letter). Can't believe people are quibbling about the accuracy of the shading instructions - get a life, really!
Also enjoyed 4409, after initially thinking it would defeat me utterly when I couldn't get anything in quadrant A. Got started with 31A, worked out what was going on in that quadrant, and worked outwards from there. Liked the appropriate nature of the extra theme words. Really satisfying puzzle.