Thank you very much Prospero. The abbreviation that was needed didn't cross my mind.
It's a pity that the superfluous letters could not have been incorporated into the grid in some way so as to penalise solvers like me who inserted the right answers (presumably) without really understanding why. It might be a difficult undertaking but I have a vague memory of it being done in the past. The great Araucaria would have relished the challenge, I'm sure.