The Preamble:
Different groups (a) – (e) may be deduced in different ways: (a) unclued entries make up the largest; (b) from each column except the first, a single letter must be copied into the bottom row (affected entries have normal clues and real words would be formed were the letters to be removed); (c) extra (single or double) letters given by wordplay in remaining clues; (d) the penultimate is revealed by reading the first letters of normal clues; (e) the extreme example must be highlighted (19 cells, symmetrically placed) after filling in the remaining blank cell.