I'm confused so can I clarify my understanding of the instructions?
"Fourteen solutions are derived from seven common word pairs, each having a single letter interchanged".
Does that mean that, having got a pair of answers, a single letter is swapped between the two answers before entering them into the grid? Or is it the 'original' word pairs (from which the solutions are derived) which have their letters interchanged, and the solution words are entered into the grid unchanged?
I almost can't be bothered doing this month's Genius :-(