To my surprise I think I have the solution: many thanks to ionacarr for a number of very nicely judged hints. To return to a previous post (number 69), I agree that it’s the first possibility that’s required and that the resulting completed grid won't show evidence that the solver has actually worked everything out: however, for a correct submission on this basis, the solver would have to choose the correct replacement in each of the 37 other pairs and only extraordinarily lucky guesswork alone would achieve that. I hope that the view would be taken that having the correct replacement in 37 out of 38 cases provides undeniable evidence that the solver has achieved sufficient understanding.