This is the hint.
This is our first book of general knowledge crosswords, and it contains fifty puzzles including the first ones of this kind to appear in The Sunday Times. The regular series of general knowledge crosswords began on April 17, 2016, when our puzzle content increased substantially, but there were previous ones as part of extra puzzle content in various holiday periods. The first of these appeared in a four-week “Spring Puzzle Special” series in May 2014. They were set by Dean Mayer, who was already writing concise and cryptic crosswords for us, and we decided to have an overall theme, which was reflected in their title — “Four Seasons General Knowledge Crossword”. That’s all our readers saw apart from the grids and clues, so I’ll leave you to discover exactly how the theme works, in puzzles 1-4. Puzzle 5 was written for a Christmas puzzle supplement in 2015, and also has an appropriately seasonal theme. It was set by Tom Johnson who edits The Spectator and New Statesman crosswords and sets cryptic and general knowledge crosswords in various newspapers and magazines.
The weekly series started with puzzle 6, the first crossword in the Sunday Times puzzle pages to be set by me. Like most of the remaining puzzles in this book, there is no theme involved. Dean, Tom and I all contribute to the weekly series, but as the puzzles are published anonymously and often changed more by the editor than our other crosswords, they remain here, and the setters don’t work in the ABCABC sequence that you can detect from the named setters for our cryptic crosswords. There is one other person involved — our Puzzles Editor David Parfitt, who test-solves and edits the ones I set.
Apart from one puzzle omitted as it seemed a bit too difficult, all of the remaining puzzles appear in their original order. Puzzle 23 has a theme, as do puzzles 29 (which was no. 25 in the weekly series), 32 and 41. Puzzle 41 has not appeared in print before, as it was included in a digital-only edition on Christmas Day, 2017. As we sometimes use clues about recent or upcoming events, and answers to clues like “Current men’s 800m world record holder” change over time, the publication date is shown for each puzzle.
Although the style of these puzzles has evolved since these ones appeared, I have resisted the temptation to amend them, except to clear up a few mistakes discovered after their original appearance, tidy up some minor house style points, clarify a few clues, and remove some repetition of similar clues for the same answer, which may be more noticeable in a book than a weekly newspaper. The puzzles are challenging, and I don’t think I would count some use of reference books or the internet as “cheating”. Alternatively, you may wish to treat them as a crossword version of a quiz night, and solve with relatives and/or friends as a team. I would like to thank my Times Crossword Championship marking room colleague Roger Phillips for proofreading the puzzles, but as the editor, reponsibility for any mistakes is mine.